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Numerical simulations of two-dimensional inviscid detonations for a stoichiometric propane/oxygen gas mixture are performed using a detailed chemical reaction model. The UC San Diego model which includes 57 chemical species and 268 elementary reactions is mainly used in the present study. It is shown that a grid size of 3 µm can capture important features such as the unburned gas pocket behind the detonation when compared to larger grid sizes. The effects of channel width show that the detonation propagates with the CJ (Chapman–Jouguet) velocity for all cases and for more than 100 times the channel width of 4.5 mm. Increasing the channel width results in an irregular detonation cell structure. A transverse detonation forms with cross-hatching marks on the maximum pressure history. The irregular detonation cell structure forms because both the reduced activation energy and the stability parameter have a value of approximately 10; however, the maximum thermicity in the detonation is one. The free radicals C3H7 and H2O2 play an important role in the propane oxidation under the high temperature in the detonation. The maximum concentration exists at a temperature of 2000–3000 K. The fifth-order WCNS (weighted compact nonlinear scheme) scheme can resolve the contact surface and complicated flow structure behind the detonation front compared to the second-order MUSCL (Monotonic Upstream-centered Scheme for Conservation Laws). [ABSTRACT FROM AUTHOR]

• Hydrocarbon (HC) oxidations were tested over Pd-only, Pt-only, and Pt–Pd catalysts. • Activity tests were performed under both near-stoichiometric and fully lean conditions. • Pd was oxidized under fully lean condition, while Pt preserved its oxidation state. • Synergistic effect of bimetallic Pt–Pd was observed under fully lean condition. Effective control of hydrocarbon (HC) emissions at low temperatures is critical for emission compliance, since a large fraction (typically 70–80%) of tailpipe HC emissions occurs during the first couple of minutes after an engine cold-start. The oxidation of propane, iso-pentane and propylene was investigated over Pd-only, Pt-only and Pt–Pd catalysts aged under lean-rich cycling conditions. Various characterizations such as XRD, XANES, STEM, CO chemisorption and H 2 -TPR were performed over the initial catalysts. Moreover, before and after the reaction, the states of the catalysts were characterized by XRD, XANES and STEM. The oxidation activity tests were carried out under both near-stoichiometric and fully lean conditions in the feedstream containing HC, O 2 , CO, H 2 , NO and H 2 O. Under the near-stoichiometric condition, the Pt/Al 2 O 3 catalyst showed much higher activity for propane oxidation than the Pd/Al 2 O 3 and Pt–Pd/Al 2 O 3 catalysts. For propylene oxidation, on the other hand, the Pd/Al 2 O 3 catalyst was the most active, and the Pt/Al 2 O 3 catalyst exhibited the lowest activity due to the fact that the co-presence of CO and propylene on the Pt surface leads to their competition for a limited amount of adsorbed oxygen. Under the fully lean condition, metallic Pd in the Pd/Al 2 O 3 catalyst was gradually oxidized to PdO and consequently poisoned by H 2 O, whereas there was little change in the state of the Pt/Al 2 O 3 catalyst, indicating higher stability of metallic Pt than Pd. However, a drastic decrease in the propane oxidation activity was observed over Pt/Al 2 O 3 in the presence of excess oxygen in the fully lean feed since preferential adsorption of oxygen on the Pt surface inhibited propane adsorption and thus the oxidation reaction. In addition, the propylene oxidation activity under the fully lean condition was greatly enhanced over all three catalysts compared to that observed under the near-stoichiometric condition, with Pd/Al 2 O 3 still being more active than Pt/Al 2 O 3. The catalyst activity for iso-pentane oxidation was affected only to a relatively small extent by the high oxygen concentration, so that the same activity order among the catalysts (Pt > Pt–Pd > Pd) was observed under both the slightly lean and fully lean conditions. These results indicate that both hydrocarbon type and oxygen concentration level are important factors determining the relative oxidation activities of the various noble metal catalysts. Relatively small beneficial effects of Pt–Pd alloying were observed during iso-pentane oxidation at low temperatures under the near-stoichiometric conditions and during propane oxidation at high temperatures under the fully lean condition. However, alloy formation was found to be detrimental for the propane oxidation under the slightly lean condition. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MnNi x oxides with irregular pits were synthesized via hydrothermal method. • The addition of Ni into MnO 2 promoted the catalytic activity for propane oxidation. • The MnNi 0.09 sample could convert 90% propane at 220 °C. • The MnNi 0.09 sample with pits exhibited the lowest apparent activation energy (33.6 kJ mol−1). Abstract Series of nickel doping MnO 2 with irregular surface pits were synthesized and employed for propane deep oxidation. The partial substitution of Ni for Mn resulted in the formation of structural defects, which could be observed by high-resolution transmission electron microscopy. The MnNi 0.09 sample exhibited the best catalytic activity for propane oxidation with the conversion of 90% at 220 °C. The presence of pits on the MnNi 0.09 sample could facilitate the dissociation of propane and mobility of oxygen along the conduction channels of surface pits, thus promoting the catalytic efficiency. Moreover, the in situ studies found that different intermediates were formed on the MnO 2 and MnNi 0.09 catalysts during the propane oxidation process. The propane was oxidized to propanoyl species on the surface of MnO 2 catalyst, while it was oxidized to hydrogen carbonates and carbonates on the surface of MnNi 0.09 sample, which were thermally less stable and converted into CO 2 at lower temperature. The finding provides a new perspective on understanding the effect of cation doping. [ABSTRACT FROM AUTHOR]

Abstract In this study, the cobalt-cerium spinel oxides catalysts were prepared via a citric acid complex method. The catalytic performance and physicochemical properties of the samples for deep propane oxidation were evaluated. Co 2 Ce 1 O x catalysts exhibit the superior low temperature activity with a T 50 value of 220 °C, which is much lower than both individual cobalt and cerium oxides. The results show that cerium ions could enter into the spinel-type lattice of the cobalt oxides and lead to the severe lattice distortion. The activated Co O bonds favor the propane activation and enhance the reducibility of active Co3+ species. Meanwhile, high proportion of Co3+ content and better oxygen mobility are also observed in the cobalt-cerium spinel oxides catalysts. The kinetic and the transient experiments reveal that the reduction step of the catalysts plays a crucial role in the deep catalytic propane oxidation. The reaction rate of Co 2 Ce 1 O x catalyst reaches 0.22 μmol g−1 s−1 at 200 °C and its activation energy is the lowest (57.9 kJ mol−1). All the results indicate that the combination of redox behaviors of Co 3 O 4 and oxygen vacancies of CeO 2 offer useful support for catalysts design toward propane oxidation at low temperature. Graphical abstract Unlabelled Image Highlights • Catalytic propane oxidation was performed over cobalt-cerium spinel oxides catalysts. • Co 2 Ce 1 O x showed the highest low temperature activity. • Reduction step of the catalysts is crucial for catalytic propane oxidation. • Proportion of Co3+ is linear with the reaction rates at 200 °C. [ABSTRACT FROM AUTHOR]

The synergy between active Pt species and ceria results in the presence of more coordinately unsaturated Pt2+ and Pt4+ species, which were found to be critical to drive C− and C−H bonds activation and enhance propane oxidation. Surface lattice oxygen on ceria in the vicinity of electron‐deficient Pt species provides the enhanced reactivity for low‐temperature propane oxidation. The reducibility and amount of activated surface oxygen species play a significant role in improving the reaction rates of propane oxidation in the 150∼300 °C temperature range. Ceria effectively promotes oxidative redispersion of platinum crystallites supported on alumina during propane oxidation in O2‐rich conditions, due to the unique ability to trap and stabilize ionic platinum. [ABSTRACT FROM AUTHOR]

Microbial anaerobic oxidation of hydrocarbons is a key process potentially involved in a myriad of geological and biochemical environments yet has remained notoriously difficult to identify and quantify in natural environments. We performed position-specific carbon isotope analysis of propane from cracking and incubation experiments. Anaerobic bacterial oxidation of propane leads to a pronounced and previously unidentified 13C enrichment in the central position of propane, which contrasts with the isotope signature associated with the thermogenic process. This distinctive signature allows the detection and quantification of anaerobic oxidation of hydrocarbons in diverse natural gas reservoirs and suggests that this process may be more widespread than previously thought. Position-specific isotope analysis can elucidate the fate of natural gas hydrocarbons and provide insight into a major but previously cryptic process controlling the biogeochemical cycling of globally significant greenhouse gases. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Porous Ba-doped Pd/γ-Al 2 O 3 hollow microspheres were synthesized by a facile method. • The porous structure and hollow microspheres were due to lysine and NH 4 HCO 3. • Porous Pd/Ba-γ-Al 2 O 3 showed enhanced activities toward CO and C 3 H 8 oxidation. Abstract Porous Ba-doped Pd/γ-Al 2 O 3 hollow microspheres were successfully synthesized via a simple hydrothermal method with the assistance of lysine, barium and NH 4 HCO 3. The introduction of lysine and NH 4 HCO 3 is beneficial to the formation of porous hollow microspheres and the promotion of specific surface area. The addition of BaO effectively improves the surface basicity of catalysts. The obtained porous Pd/Ba-γ-Al 2 O 3 hollow microspheres are about 5–6 μm in diameter and shell thickness of 1 μm. The porous Pd/Ba-γ-Al 2 O 3 hollow microspheres also exhibit higher catalytic activity for CO and C 3 H 8 oxidation compared with the one without adding lysine and NH 4 HCO 3. [ABSTRACT FROM AUTHOR]

Abstract: Self-sustained reaction rate oscillations in the oxidation of propane and in the propane steam reforming with oxygen over nickel foil have been studied in situ by near-ambient pressure X-ray photoelectron spectroscopy and mass-spectrometry. It was found that regular relaxation-type oscillations in both reactions proceed under similar conditions. In the former case, the peaks of CO, CO2, H2, and H2O were detected by mass-spectrometry as gas-phase products. In contrast, in the latter case, after addition of water to the reaction feed, the mass-spectrometric signal of water decreased simultaneously with the signals of O2 and C3H8, whereas the signals of CO, CO2, and H2 increased. It means that in the presence of water in the reaction feed, the propane steam reforming proceeds with a significant rate. In both cases, the oscillations arise due to spontaneous oxidation and reduction of the catalyst. According to the Ni2p and O1s core-level spectra measured in situ, the high-active catalyst surface is represented by nickel in the metallic state, and the transition to the low-active state is accompanied by the growth of a NiO film on the catalyst surface. The oscillations in the gas phase are accompanied by oscillations in the catalyst temperature, which reflects proceeding endothermic and exothermic processes. An oscillatory mechanism, which can be common for oxidative catalytic reactions over transitional metals, is discussed.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Copper oxide catalysts supported on nanostructured silica SBA‐15 were synthesized with varying copper loadings in a range from 1.1 to 19.4 wt.%. Catalysts were structurally characterized by N2 physisorption, X‐ray diffraction and ex situ as well as in situ diffuse reflectance UV‐Vis spectroscopy. Copper oxide species contained Cu2+ in an octahedral configuration with a tetragonal distortion. Increasing the copper loading resulted in a decreasing optical band gap, which is associated with a growing particle size. Additionally, CuO/SBA‐15 samples were examined by temperature‐programmed reduction confirming a narrow particle size distribution. Structural evolution and catalytic activity were investigated during selective oxidation of propene focusing on product distribution of nucleophilic and electrophilic oxidation. Catalytic testing was carried out using an on‐line GC and MS coupled to a laboratory fixed‐bed reactor. All catalysts selectively oxidized propene to acrolein and propylene oxide (PO). With time on stream activity decreased while selectivity towards acrolein and PO increased. While selectivity towards PO increased with copper loading and, hence, copper oxide particle size, selectivity towards acrolein was largely independent of copper loading. Cu on the dark side of the moon: Copper oxide nanoparticles supported on SBA‐15 are active catalysts in propene oxidation to acrolein and epoxidation to propylene oxide. Varying particle sizes of supported copper oxide nanoparticles affects catalytic performance. While allylic oxidation to acrolein is independent of particle size, nucleophilic epoxidation to propylene oxide strongly correlates with particle size. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vanadium supported on activated carbon by using sugarcane straw as raw material is investigate for the first time. • Surface vanadium density far below the monolayer coverage was investigated towards propane oxidation. • Sugarcane straw produces an activated carbon with similar properties of thecommercial Alphacarbo. • The possibility of waste (sugarcane straw) valorization opens a range of catalytic application opportunities. • Highly dispersed vanadium carbon based catalyst are capable to activate propane molecule to produce propene. A high surface area activated carbon was obtained from sugar cane straw by chemical activation with phosphoric acid and was used for the first time as a support for vanadium catalysts. This work aims to investigate the vanadium oxide species in a low surface density (up to 1 V atom nm−2) on this new support, especially applied to propane oxidation reaction. Moreover, commercial activated carbon materials were used as support for comparison. The discussion is conducted in terms of catalyst textural properties, nature and concentration of surface vanadium oxide species, surface functional groups, and their structure/reactivity relationship. All samples were characterized by adsorption-desorption of N 2 (BET), scanning electron microscopy, coupled with energy dispersive microscopy (SEM-EDS), thermal analysis (TG-DTA), Boehm titration, ammonia thermo desorption (NH 3 -TPD), X-ray photoelectron spectroscopy (XPS), Laser Raman spectroscopy (RS) and X-ray diffraction (XRD). The obtained results show that vanadium oxide species, even at a very low density, are capable of converting propane (30%), producing propylene (10%), but still producing a high amount of CO x products. However, it is worth noting that V-P bonds are the key factor for the Oxidative Dehydrogenation of Propane activity. [ABSTRACT FROM AUTHOR]

Selective removal of CO from the effluent streams in real‐life chemical processes is of great importance in many different fields of industry. Until now it remains challenging to use non‐precious metal oxides to selectively remove CO at low temperatures from real‐life chemical effluent with complex compositions. Herein, a series of binary and ternary transition metal oxide catalysts were prepared by co‐precipitation method and employed for the preferential removal of CO in the effluent stream (off‐gas) of propane selective oxidation. It was found that the CuO−CeO2−based mixed oxide catalyst exhibited the best CO removal performance, wider operating temperature window and higher resistance to the inhibition of hydrocarbons, H2O and CO2. The presented catalyst showed high potential for selective removal of CO in the off‐gas stream containing CO2, H2O and various hydrocarbons. Full st(r) eam ahead! For selective removal of CO in off‐gas stream with complex compositions from real‐life propane oxidation, CuO−CeO2−based catalysts exhibited the excellent CO removal performance, wider operating temperature window and excellent resistance to the inhibition of H2O, CO2 and hydrocarbons. The most active sites for high CO selective removal appeared to only locate at CuO−CeO2 interface. [ABSTRACT FROM AUTHOR]

Kinetics of oxidation of diols (glycerol and 1, 2-propanediol) by hexavalent chromium was studied in aqueous acetic acid perchlolric acid mixtures. The reactions were first order with respect to oxidant and substrate concentrations. Whereas, reaction showed second order by varying acid concentration. With the change in the concentration of manganous ion and solvent composition change in the rate of reaction was observed. In these oxidation reactions an increase in rate was observed with decrease in dielectric constant pointing to the fact that these are reactions between positive ion and dipolar. Arrhenius parameters were computed and a plausible mechanism was postulated based on experimental results. [ABSTRACT FROM AUTHOR]

Graphical abstract Acid leached Co 3 O 4 nanocatalysts exhibit excellent low temperature activity toward propane oxidation independent of propane and oxygen concentrations. Highlights • Chemical leaching strategy was firstly used for boosting the activity of Co 3 O 4 nanocatalyst. • It is much more active than commercial Pt/Al 2 O 3 and Pd/Al 2 O 3 in propane oxidation. • It shows an excellent and stable C 3 H 8 oxidation independent of O 2 and C 3 H 8 concentrations. • The chemical leaching helped derive much more active sites on Co 3 O 4 nanocatalyst surface. Abstract Rational modification of interfacial structure and chemistry can help effectively tailor the reactivity and stability of heterogeneous catalysts regardless of their elemental or compound natures. Herein, a diluted acidic treatment was designed and utilized to modify the surface structure and chemistry of spinel Co 3 O 4 nanoparticles. Such a chemical leaching strategy has significantly promoted the propane oxidation activity of the PGM-free Co 3 O 4 nanocrystal aggregates. With a much higher activity than the commercial Al 2 O 3 supported Pt and Pd catalysts, these leached nanoparticle aggregates exhibited much more abundant defects, surface Co2+ and chemisorbed oxygen species. Such surface-modified Co 3 O 4 nanocatalysts have displayed excellent and stable propane oxidation efficiency independent of both O 2 and C 3 H 8 concentrations, where the activities of both commercial Pt (or Pd)/Al 2 O 3 and self-made Pt (or Pd)/CeO 2 catalysts were greatly affected by different O 2 and C 3 H 8 concentrations. Meanwhile, the Co 3 O 4 nanocrystal aggregates catalyst exhibited good performance in presence of water or sulfur dioxide. This facile chemical leaching based technique provides a potential means to make highly active and stable oxide catalysts. [ABSTRACT FROM AUTHOR]

Plagued by low surface area and limited oxidation activity at low temperature, perovskite-type LaMnO3 based catalysts also suffer from poor hydrothermal stability. In this communication, mesoporous nanotube arrays of LaMnO3-Pt were successfully derived from core/shell nanorod arrays with significantly increased surface area through diluted acid etching. Surface Mn4+ population is boosted to compensate La cation deficiency and enhance low temperature reducibility of nanotube arrays, enabling surface dispersion of abundant metallic-state Pt nanoparticles. As a result, significantly enhanced catalytic propane oxidation was achieved in such a new class of perovskite/Pt nanotube array integrated structured catalysts. [ABSTRACT FROM AUTHOR]

The catalytic properties of ZnAlVO mixed oxides derived from decavanadate-exchanged ZnAl–layered double hydroxide (LDH) precursors prepared by a sol–gel method (ZnAlVO–LDH x,y ) were investigated in the oxidative dehydrogenation of propane and compared with those of supported catalysts obtained by conventional impregnation of NH 4 VO 3 on ZnO (ZnVO-I, y ) and ZnAlO mixed oxide (ZnAlVO-I, y ) supports. The effects of composition and calcination time on the catalytic behavior were particularly examined. Higher propane conversions were achieved at higher vanadium content and calcination time of the precursors. The LDH-derived catalysts were the most active ones in all the temperature range studied (300–425 °C). The order of activity for propane conversion for the different catalyst families varies as ZnAlVO–LDH x,y > ZnAlVO-I > ZnVO-I and follows the strength of the Lewis and Brønsted acid sites determined by monitoring of pyridine adsorption by Fourier transform infrared spectroscopy, whereas the propene selectivities are close together in agreement with the similar densities of basic sites determined by CO 2 –temperature-programmed desorption measurements. It was indeed established that the acidity, rather than the nature of the crystalline phases, the reducibility, or the specific surface area of the samples, governs the catalytic activity. [ABSTRACT FROM AUTHOR]

Protein oxidation is a major pathway for degradation of biologic drug products. Past literature reports have suggested that 2,2-azobis (2-amidinopropane) dihydrochloride (AAPH), a free radical generator that produces alkoxyl and alkyl peroxyl radicals, is a useful model reagent stress for assessing the oxidative susceptibility of proteins. Here, we expand the applications of the AAPH model by pairing it with a rapid peptide map method to enable site-specific studies of oxidative susceptibility of monoclonal antibodies and their derivatives for comparison between formats, the evaluation of formulation components, and comparisons across the stress models. Comparing the free radical–induced oxidation model by AAPH with a light-induced oxidation model suggests that light-sensitive residues represent a subset of AAPH-sensitive residues and therefore AAPH can be used as a preliminary screen to highlight molecules that need further assessment by light models. In sum, these studies demonstrate that AAPH stress can be used in multiple ways to evaluate labile residues and oxidation sensitivity as it pertains to developability and manufacturability. [ABSTRACT FROM AUTHOR]

We have investigated electronic and catalytic modifications of the p-type semiconducting selective oxidation catalyst vanadyl pyrophosphate (VPP) for propane oxidation in the presence and absence of steam. Steam changes propane conversion only slightly, but increases the selectivity toward oxygenates (acrylic acid, acetic acid) and the olefin propylene resulting in reduced selectivity of the undesired total oxidation products CO and CO2. Contact-free in operando microwave conductivity measurements at 0.1 MPa revealed that the modified catalytic performance is accompanied by a reduced electrical conductivity. Surface sensitive near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and X-ray absorption spectroscopy (XAS) measurements at 25 Pa showed that steam depletes the topmost surface of VPP in phosphorus and enhances the average vanadium oxidation state slightly. These findings are accompanied by a decreased work function, but no detectable shift of the valence band edge is observed. Thus, the chemical surface modification changes the surface dipole but leaves the barrier height of the surface induced space charge layer basically unaffected. Hence, we conclude that steam does not affect the electron hole concentration (majority charge carriers) and hence the oxygen vacancy concentration. Therefore, the reduced conductivity can be understood in terms of charge carrier mobility changes, which may affect the selectivity of VPP toward oxygenates with steam. In addition, the modification of local properties, such as the concentration of acid sites as well as the nature and number of adsorption sites may have an impact on the catalytic properties. [ABSTRACT FROM AUTHOR]

Acrylic acid is an important industrial chemical, and efficient catalysts for its direct preparation by propane oxidation are highly desirable. For this purpose, neutral silica networks were introduced on the surface of MoVTeNb mixed oxide catalysts by controlled silylation using a methyl silicate oligomer (MS-51). The modified catalysts gave ∼56.5% yield of acrylic acid with a selectivity of 77.1% in the oxidation of propane at 380 °C. The catalysts were characterized by X-ray fluorescence, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller specific surface area, X-ray diffraction (Rietveld analysis), pyridine desorption, and scanning electron microscopy. MoVTeNb mixed oxide was found to be composed of 90.9% M1 phase and 2.3% M2 phase, and upon silylation, the surface was uniformly covered by a thin SiO 2 layer with 0.14 molar ratio with respect to Mo and an estimated thickness of 2.4 nm. The amount of acid sites decreased after the first three silylation cycles, but was not affected by repeated cycles. The results of the kinetic study based on the comparison of the simulated contribution of each side reaction were consistent with those of the model reactions using acrylic acid and other reactants: the controlled silylation effectively suppressed acrylic acid oxidation, especially after repeated silylation cycles, which is responsible for the superior performance of the silylated catalysts. Considering the relatively large size of acrylic acid compared to propane and the efficient propane activation by silica-covered catalysts, the controlled silylation was proposed to have two roles, by which further consecutive oxidation is prevented effectively to exhibit excellent performance in oxidation of propane: i) to block the unfavorable acidic sides, ii) to generate a silica layer with pore mouth openings on the surface of MoVTeNb mixed oxide, which allow the entrance of propane but inhibit re-entrance of the produced acrylic acid. [ABSTRACT FROM AUTHOR]

Three-dimensionally ordered macroporous (3DOM) NiCe catalysts with different Ni/Ce molar ratio were fabricated using the colloidal crystal templating method. The physic-chemical properties of the samples were characterized by various techniques, including N2 adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, and H2-temperature-programmed reduction (TPR) characterizations. The results revealed that the 3DOM NiCe samples preserved the three-dimensionally ordered macroporous channels with interlinked micro- or mesoporous structure and highly dispersed nickel oxide species in the framework upon different amount of nickel incorporation. In the evaluation of the oxidative dehydrogenation (ODH) of propane, the 3DOM NiCe catalysts exhibited higher selectivity and yield to propene than the amorphous NiCe catalyst. An optimum yield of propene of 11.9% with the 30.3% propane conversion at 375 °C was obtained over the 3DOM 2NiCe catalyst. Combining XRD, TPR, and Raman analysis, it could be found that the nickel incorporation in CeO2 lattice produced a high concentration of oxygen vacancies that were the active sites for the oxidative dehydrogenation of propane. Besides this, the 3DOM structure promoted the rapid diffusion of the reactants and products-favorable for the generation of propene in the ODH of propane. [ABSTRACT FROM AUTHOR]

One-step propane partial oxidation to acrylic acid and acrolein has been studied widely. Research on the catalyst systems has been accompanied by investigations of various reactor configurations in order to improve acrylic acid/acrolein yield for achieving industrial applications. Based on the reaction kinetics, lower gas-phase oxygen concentration supports the desired reaction path to the oxygenate products. Therefore, novel reactor concepts that can continuously provide uniform and controllable oxygen concentration have the potential for acrylic acid/acrolein yield enhancement. In this way, alternative reactor technologies from reactor structuring, fluidization to membrane type have been proposed. In this work, the actual state of these efforts is reviewed. The advantages and disadvantages of each concept are pointed out. However, the assessment of a new technology due to the numerous aspects that have to be considered is very difficult. It is suggested that circulating fluidized bed is a much preferred solution with respect to the acrylic acid/acrolein yield improvement. [ABSTRACT FROM PUBLISHER]

The phase equilibrium conditions in the (propan-2-ol + carbon dioxide + water) system were measured. The measurements were performed using the batch, isochoric method at the temperatures between 250.8 K and 265.7 K. The equilibrium pressures were measured between 0.275 MPa and 0.995 MPa, and increased with increasing temperatures. Propan-2-ol is known as thermodynamic inhibitor for hydrate formation. However at the temperatures below 262 K, the equilibrium pressures in the (propan-2-ol + carbon dioxide + water) system are lower than those without propan-2-ol (carbon dioxide + water system). The measurements indicate the formation of the hydrates containing propan-2-ol and carbon dioxide in this system. [ABSTRACT FROM AUTHOR]

The redox reaction between KMnO4 and Co(NO3)2 was designed and readily utilized for the scalable integration of spinel Mn xCo3− xO4 nanosheet arrays in three-dimensional ceramic honeycombs by controlling the reaction temperature. The Co2+ can reduce MnO4− to form Mn-Co spinel oxide nanosheet arrays uniformly on the channel surface of cordierite honeycomb. The novel platinum group metal free oxide nanosheet array integrated ceramic honeycomb monolith shows good low-temperature catalytic activity for propane oxidation, with the 50 % conversion temperature achieved at 310 °C, which is a much lower temperature than that over the wash-coated commercial Pt/Al2O3. These integrated Mn-Co composite oxide nanoarrays may hold great promise for the construction of advanced monolithic catalyst for high-performance and low-cost emission control. [ABSTRACT FROM AUTHOR]

The deep ocean and its sediments are a continuous source of non-methane short-chain alkanes (SCAs) including ethane, propane, and butane. Their high global warming potential, and contribution to local carbon and sulfur budgets has drawn significant scientific attention. Importantly, microbes can use gaseous alkanes and oxidize them to CO2, thus acting as effective biofilters. A relative decrease of these gases with a concomitant 13C enrichment of propane and n-butane in interstitial waters vs. the source suggests microbial anaerobic oxidation. The reported uncoupling of sulfate-reduction (SR) from anaerobic methane oxidation supports their microbial consumption. To date, strain BuS5 isolated from the sediments of Guaymas Basin, Gulf of California, is the only pure culture that can anaerobically degrade propane and n-butane. This organism belongs to a metabolically diverse cluster within the Deltaproteobacteria called Desulfosarcina/Desulfococcus. Other phylotypes involved in gaseous alkane degradation were identified based on stable-isotope labeling and fluorescence in-situ hybridization. A novel syntrophic association of the archaeal genus, Candidatus Syntrophoarchaeum, and a thermophilic SR bacterium, HotSeep-1 was recently discovered fromthe Guaymas basin, Gulf of California that can anaerobically oxidize n-butane. Strikingly, metagenomic data and the draft genomes of ca. Syntrophoarchaeum suggest that this organism uses a novel mechanism for n-butane oxidation, distinct from the well-established fumarate addition mechanism. These recent findings indicate that a lot remains to be understood about our understanding of anaerobic SCA degradation. This mini-review summarizes our current understanding of microbial anaerobic SCA degradation, and provides an outlook for future research. [ABSTRACT FROM AUTHOR]

Boron nitride was recently identified as a highly selective catalyst for the oxidative dehydrogenation of propane. In this communication, we report that other boron-containing materials such as boron carbide, titanium boride, nickel boride, cobalt boride, hafnium boride, and tungsten boride, as well as elemental boron itself, show the same exceptional behavior as boron nitride. X-ray photoelectron and infrared spectroscopy suggest oxyfunctionalization of the surface. This observation disproves previous mechanistic hypotheses that edge sites on the boron nitride would be the active sites and rather suggests the formation of an analogous surface-stabilized BO x active site for all tested boride catalysts. [ABSTRACT FROM AUTHOR]

The oxidation of propane has been studied over silica-supported vanadium oxide and polycrystalline, bulk MoVTeNb oxide with M1 structure. Temperature-programmed reaction experiments were performed, and the reactivity of propane molecules labeled with deuterium and 13C, respectively, was analyzed under steady-state conditions. The measurement of kinetic isotope effects reveals fundamental differences in the activation of propane over the two catalysts. The reaction network of consecutive and parallel reactions of the formed propylene is comparable. However, oxygen insertion into the CHO group of acrolein under formation of acrylic acid is faster over M1 than oxidation at the CH2 group and decarbonylation to acetaldehyde. In contrast, the latter process is preferred over silica-supported vanadium oxide resulting in lower selectivity to unsaturated oxygenates. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization, and enhanced propane dehydrogenation properties of hierarchical Ga-MFI zeolite catalysts synthesized by two different methods: (i) repetitive branching and (ii) utilization of a long chain alkyl SDA. Structural, compositional, and morphological characterizations confirm that the Ga-MFI catalyst materials have hierarchical structures including micropores and mesopores in a single particle and show that Si/Ga ratios comparable to bulk Ga-MFI catalysts can be obtained. Acid site analysis using NH3-TPD and pyridine adsorption followed by in situ IR spectroscopy allowed quantification of the number and types of acid sites present and show that the hierarchical catalysts have considerably higher Lewis acid site concentrations than the bulk catalysts. The hierarchical Ga-MFI catalysts show superior PDH performance (at 600 °C) compared to bulk Ga-MFI catalysts. Propane conversion rates are increased 2-6-fold and propylene selectivities are 10-100% higher. We also examine the effects of synthesis variations--such as addition of 3-mercaptopropyltrimethoxysilane during synthesis and H+ ion-exchange--and find that both these steps have a beneficial effect on PDH properties. Calculations suggest that PDH in both the bulk and the hierarchical Ga-MFI is not diffusion-limited. Therefore, the superior performance of hierarchical Ga-MFI is due to intrinsically higher activity and selectivity. Potential reasons for this behavior are outlined. The present findings showing enhancement of PDH in hierarchical Ga-MFI catalysts suggests that the utility of the hierarchical zeolites is not limited to diffusion-limited reactions involving large, bulky molecules and that they may be useful in more diverse applications involving gas-phase reactions with small molecules. [ABSTRACT FROM AUTHOR]

The study aims at proposing a skeletal mechanism of propane oxidation that describes low-temperature combustion and predicts major hydrocarbon product formation in nonpremixed flames. Utilizing a combination of a sensitivity analysis and path flux analysis, we refine and minimize a recently proposed detailed mechanism of UC San Diego (Prince et al., 2017) without empirical adjustments of rate constants for elementary reactions. The skeletal mechanism with 33 species and 122 reactions improves accuracy for autoignition calculations in the negative temperature coefficient region and its size is commensurate to numerical grids used in solutions of computational fluid dynamics with detailed kinetics. For the first time, the previously measured temperature, major products and non-fuel hydrocarbons in diffusion flames of propane associated with counterflow and coflow configurations are, respectively, verified by means of 1-D kinetic modeling and 2-D computational fluid dynamics. A comprehensive analysis of decomposition pathways connected with preserved and removed reactions provides a clear foundation for mechanism developers to build mechanisms of other alkane fuel oxidation. The rate of production analysis interprets how the experimentally measured propene and 1-butene are formed earlier than acetylene and propyne in the coflow flame. Moreover, the present skeletal mechanism, compared with published detailed mechanisms, features a significant reduction in computational cost. [ABSTRACT FROM AUTHOR]

Computations of cup-burner flames in normal gravity have been performed using propane as the fuel to reveal the combustion inhibition and enhancement by the CF 3 Br (halon 1301) and potential alternative fire-extinguishing agents (C 2 HF 5 , C 2 HF 3 Cl 2 , and C 3 H 2 F 3 Br). The time-dependent, two-dimensional numerical code used includes a detailed kinetic model (up to 241 species and 3918 reactions), diffusive transport, and a gray-gas radiation model. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilizes a trailing flame, which is inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of agent in the coflow increases gradually, the premixed -like reaction kernel weakens, thus inducing the flame base detachment from the burner rim and blowoff-type extinguishment eventually. The two-zone flame structure (with two heat-release-rate peaks) is formed in the trailing diffusion flame. The H 2 O formed in the inner zone is converted further, primarily in the outer zone, to HF and CF 2 O through exothermic reactions most significantly with the C 2 HF 5 addition. The total heat release of the entire flame decreases (inhibiting) for CF 3 Br but increases (enhancing) for the halon alternative agents, particularly C 2 HF 5 and C 2 HF 3 Cl 2 . Addition of C 2 HF 5 results in unusual (non-chain branching) reactions. [ABSTRACT FROM AUTHOR]

Several CeO2 and CuO-CeO2 catalysts were prepared using different methods, i.e., a homogeneous precipitation with urea, a nanocasting route using CMK-3 carbon as a hard template and a sol-gel process using Poly(methyl methacrylate) (PMMA) polymer as a soft template, and tested in the total oxidation of propane. The catalysts were characterized by a number of physicochemical techniques (XRD, N2 adsorption, TPR, XPS, Raman spectroscopy) showing distinct characteristics. For each series, Cu-Ce-O catalysts with low Cu-loadings (5 wt % CuO) showed the highest activity, higher than those samples either without copper or with high Cu-loading (13 wt % CuO). The incorporation of copper leads to an increase of the concentration of bulk defects but if the Cu-loading is too high the surface area drastically falls. The highest activity in the total oxidation of propane was achieved by Cu-containing ceria catalysts synthesized using a polymer as a template, as this method yields high surface area materials. The surface area and the number of bulk/sub-surface defects of the ceria seem to be the main properties determining the catalytic activity. [ABSTRACT FROM AUTHOR]

Nanostructured hybrid materials made of guest ions and a self-assembled copolymer were used as precursors for the preparation of NiMo-based catalysts. The hybrids were calcined in air and the recovered materials were characterized and tested in propane oxidative dehydrogenation. A 6-fold improvement of the yield to propene is obtained as compared with classically prepared catalysts. The exothermic degradation profile of the copolymer is the key point of our approach as it allows to prepare a porous β-NiMoO 4 , namely the phase particularly desired for its superior propene selectivity. More precisely, the polar backbone and the aliphatic side chains of the copolymer burn at different temperatures. The former ignites at moderate temperatures and initiates the early crystallization of β-NiMoO 4 . Occurring at higher temperature, the decomposition of the aliphatic part then induces the formation of mesopores. A β-NiMoO 4 can thus be prepared at moderate temperatures whereas elevated calcination temperatures (>650 °C) are usually required. This peculiar behavior enables to prevent the texture of NiMoO 4 from sintering and to maintain at high levels its mesoporosity, specific area and thus catalytic activity. At the end, the use of our tailor designed copolymer template allows reaching the remarkably high propene yields obtained. [ABSTRACT FROM AUTHOR]

Reforming of propane for the production of syngas can improve the utilisation of petroleum products in chemical and energy processes as it is a major constituent in refinery gas. The search for catalytic and selective membranes for the efficient conversion of natural gas with carbon higher than methane is very attractive and remains challenging. Since Pr 2 Ni 0.75 Cu 0.25 Ga 0.05 O 4 possesses high mixed conductivity and oxygen permeation properties, it is extensively investigated for potential application for oxygen membrane reforming of propane in this study. The membrane is coated with La 0.5 Sr 0.5 CoO 3 and Ni catalysts to achieve surface activity for oxygen dissociation and propane oxidation, respectively. The propane reforming efficiency of the membrane specimens with a 0.3 mm thickness are studied as a function of temperature (800–1000 °C), using N 2 :C 3 H 8 :O 2 reactant gases with three mixing ratios of 90:7:3, 80:14:6 and 70:20:9 at flow rate of 50–375 ml/min. Over 99% of propane conversion is achieved at every gas flow rate tested. The reaction products are H 2 , H 2 O, CO, CO 2 , CH 4 , C 2 H 6 , C 2 H 4 , C 3 H 6 , C 4 + , and coke with the highest yield of CO and H 2 (37 and 29%, respectively), are obtained at 900 °C using the gas flow rate between 225 and 275 ml/min. The oxygen permeation rate observed at this condition is in the range of 1600–1900 μmol/cm 2 /min. These results suggest that the utilisation of Pr 2 Ni 0.75 Cu 0.25 Ga 0.05 O 4 is promising as an oxygen membrane in the reforming of propane to syngas. [ABSTRACT FROM AUTHOR]

The growth of oxygenated carbonaceous (oxy-carbon) species on the surface of Pt/Al 2 O 3 during total oxidation of propane is analyzed in detail—including their composition, their location on the catalyst surface, their reactivity, and their role in the propane oxidation mechanism—by in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Platinum nanoparticles catalyze the transformation of propane into many different oxy-carbon surface species, including acetate, enolate, aliphatic ester, and acetone, which spillover and grow on the Al 2 O 3 support. There is no correlation between the concentration of oxy-carbon surface species and the rate of CO 2 production in the gas-phase, which indicates that these species are inert spectators in the propane oxidation mechanism. Temperature-programmed oxidation of the oxy-carbon surface species reveals that enolate, aliphatic ester, and acetone species are removed from the surface by combustion at similar temperatures with an activation barrier of 112 kJ/mol, whereas acetate species are removed at higher temperatures with an activation barrier of 147 kJ/mol. Both the formation and combustion of oxy-carbon surface species occur in pathways that are parallel to, and orders-of-magnitude slower than, the main pathway to CO 2 production. [ABSTRACT FROM AUTHOR]

Fe-containing ZSM-5 catalysts are reported to be efficient catalysts for the partial oxidation of propane to oxygenated products at reaction temperatures as low as 50 °C in an aqueous phase reaction when using the green oxidant H2O2. It was previously proposed that extra framework Fe species at the exchange sites of the zeolite are responsible for activation of both the alkane and hydrogen peroxide. Through a systematic study of the influence of framework topology and exchange properties, it is now shown that this high catalytic activity is specific to the MFI-type Brønsted acidic zeolite ZSM-5. Furthermore, through a simple aqueous acid washing treatment, leaching of approximately 77 % of iron present within a Fe/ZSM-5 catalyst only caused the relative propane conversion to decrease by 17 %; implying that most of the initially loaded Fe does not actually contribute to the catalytic activity. This small change in conversion after 'excess' Fe removal, amounts to a three-fold increase in turnover frequency (TOF) (Fe) from 66 h−1 to 232 h−1 compared with the parent Fe/ZSM-5 catalyst. By comparing these samples, it is shown by NH3 temperature-programmed desorption, 27Al magic angle spinning NMR spectroscopy, X-ray photoelectron spectroscopy and TEM analysis that surface iron oxide species are effectively spectators in the oxidation of propane with H2O2. This provides further insight as to the location and true nature of the catalytically active Fe species. [ABSTRACT FROM AUTHOR]

The series of Pd/AlO supported catalysts with different sizes of palladium particles has been prepared and studied in total propane oxidation under various conditions. The preparation method provides a variation of the Pd particle sizes within the range of 3-6 nm and core-shell distribution of the palladium particles on alumina granules. It has been observed that an increase in Pd particle sizes leads to a parallel increase in turnover frequency (TOF) values in total propane oxidation. Both propane-to-oxygen ratio and temperature also affects the catalytic activity. Chemical state of palladium in the catalysts has been studied under the reaction conditions using in situ XPS. It has been shown that both the metallic and oxidized Pd species coexist on the catalyst surface during the propane oxidation reaction. Remarkably, evident linear correlation between TOF values and Pd/Pd ratios has been revealed. [ABSTRACT FROM AUTHOR]

Nanosized cobalt oxides were synthesized by ammonia-etching of cobalt hydroxide and subsequent calcination. The effects of ammonia etching on the structures and catalytic properties of cobalt oxide were investigated. The results suggested that the cobalt oxide is composed of cubic CoO having particle sizes in the range of 10-20 nm; smaller than the analogue prepared through the conventional precipitation method. Ammonia etching improved the reducibility of cobalt oxide, and facilitated the generation of surface oxygen vacancies and the production of surface-adsorbed active oxygen species. The activity of CoO in propane oxidation was greatly enhanced by ammonia etching, mainly due to the smaller particle size and better redox properties. The facile ammonia-etching synthesis method has potential for large-scale and low-cost production of cobalt oxide catalyst. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The authors present the results of investigation and experimental implementation of several processes: production of heavy oil residue and its deasphaltizing and impregnation of carbonate rock with deasphalted oil. Heavy oil residue has been produced during fractionation of highly-vicious oil by steam-thermal method. Deasphaltizing of oil-residue and impregnation of carbonate rock are implemented with the use of extraction and supercritical fluid impregnation processes with propane-butane solvent. [ABSTRACT FROM PUBLISHER]

Propane partial oxidation to synthesis gas at various feed conditions was investigated over nickel catalysts supported on high surface area γ-alumina. The physicochemical characteristics of the calcined, reduced and spent samples were determined by TPR, BET, XRD, TPO and SEM analyses. The influences of Ni content, reduction and reaction temperatures, gas hourly space velocity (GHSV) and feed ratio on the catalytic properties were investigated. The activity measurements revealed that the propane conversion had a direct relation with reaction temperature and nickel loading and increased with increasing of both these factors. However, there was an optimum value for nickel content and reaction temperature in which the H 2 and CO yields were maximum. The 7.5 wt% Ni/Al 2 O 3 exhibited high stability for 12 h without any decrease in activity. However, the selectivity declined gradually with reaction time due to carbon formation. The TPO analysis revealed that an increase in O 2 /C molar ratio from 0.25 to 0.75 caused a decrease in the amount of deposited carbon. Also, the amount of accumulated carbon slightly decreased with rising the reaction temperature. These results were confirmed by the SEM analysis and the filamentous carbon was observed on the catalyst surface. In addition, the increase in reduction temperature caused an increase in C 3 H 8 conversion and H 2 /CO ratio. [ABSTRACT FROM AUTHOR]

Surfactants are classified on the basis of the nature of the hydrophilic groups. Surfactant micelle represents a tiny template or nanoreactor which is generally used for preparing nano-structured materials of desired sizes and shapes with required functionalities. In this present investigation chromic acid oxidation of 1.3-propanediol (1.3-PDO) to 3-hydroxy propionaldehyde (3-HPA) was carried out by using four representative promoters: picolinic acid (PA), 2.3-pyridine dicarboxylic acid (2.3 diPA), 2.2′-bipyridine (bipy) and 1.10-phenanthroline (phen) in presence and absence of surfactants sodium dodecylsulphate (SDS), N -cetylpyridinium chloride (CPC) and Triton-X-100 (TX-100). Reactions were performed under pseudo-first-order condition: [1.3-PDO] T ≫ [Cr(VI)] T in aqueous media at 30 °C temperature. Different combinations were performed to select the suitable combination of promoter and micellar catalyst for this oxidation. Based on the kinetic results, combination of TX-100 and phen was found to be the most suitable one for this oxidation. The mechanisms of both unpromoted and promoted reaction paths were proposed. The product was confirmed by 2.4-DNP test followed by FTIR spectroscopy of the hydrazone derivative. [ABSTRACT FROM AUTHOR]

Diesel-ignited propane dual fuel low temperature combustion was characterized in a single-cylinder research engine (SCRE) at constant values of indicated mean effective pressure (IMEP of 5.1 bar), engine speed (1500 rpm), and propane energy substitution (PES = 80%). The effects of three important engine parameters (start of injection (SOI) of diesel fuel, common-rail pressure (P rail ) for diesel injection, and boost pressure (P in )) on engine performance, combustion, and emissions were examined. As SOI was advanced from 355 absolute crank angle degrees (CAD) (or 5° BTDC) to 280 CAD for constant P rail = 500 bar and P in = 1.5 bar, the apparent heat release rate (AHRR) profiles changed from a two-stage, “diesel-like” combustion process to a smooth, “Gaussian-like,” single-stage combustion process, that was representative of more homogeneous combustion. In addition, with SOI advancement, the combustion phasing (CA50) was initially advanced but eventually occurred later for very early SOIs. Indicated-specific emissions of oxides of nitrogen (ISNOx) were reduced to about 0.12 g/kW h for SOIs advanced beyond 310 CAD while maintaining high indicated fuel conversion efficiencies (IFCEs). While smoke emissions were below 0.1 FSN for all conditions tested in this study, indicated-specific hydrocarbon (ISHC) and carbon monoxide (ISCO) emissions were high at both very early and very late SOIs. Efficiency-emissions tradeoffs indicated an “optimal” SOI of 310 CAD under these conditions, which was chosen for further studies at different P rail and P in . Decreasing P rail from 1300 bar to 200 bar at P in = 1.5 bar led to a steep increase in ISNOx emissions for P rail below 400 bar; however IFCE and smoke were relatively invariant with P rail . Boost pressure effects were then quantified at P rail = 500 bar. As P in was increased from 1.1 bar to 1.8 bar, the ignition delay decreased and the AHRR profiles continued to exhibit single-stage combustion, albeit with different rates and peak magnitudes. Moreover, with increasing P in , the IFCE and ISCO increased while ISNOx and ISHC decreased slightly. Finally, the impact of SOI, P rail , and P in variations on engine stability (i.e., COV of IMEP), maximum pressure rise rates (MPRRs), and combustion duration were also characterized. [ABSTRACT FROM AUTHOR]

The use of advanced combustion technologies (MILD, oxy-fuel combustion) is among the most promising methods to reduce emission of pollutants, as the system working temperatures are enough low to boost the formation of several classes of pollutants. To access this temperature range, a significant dilution of reactants is required. At the same time, reactants have to be preheated to sustain the oxidation process. Such conditions are achieved by a strong recirculation of exhausted gases. Such a strategy implies that high contents of CO 2 and/or H 2 O interact with the reactants oxidation chemistry. In order to characterize this aspect of the combustion processes under diluted conditions, experimental tests were carried out for propane/oxygen/nitrogen mixtures in presence of variable amounts of CO 2 in a quartz Jet Stirred Flow Reactor (JSFR). Experiments were realized at atmospheric pressure, over the temperature range 720–1100 K, from fuel lean to rich conditions and at a residence time of 0.5 s. Temperature and species concentration measurements suggest that the oxidation of propane is significantly altered by CO 2 in dependence of mixture inlet temperatures and equivalence ratios. Numerical simulations pointed out that kinetic models are not able to correctly reproduce the experimental results. Further numerical analyses were performed to explore the interaction of CO 2 with the oxidation chemistry of propane. Results suggested that such a species alters the main radical branching mechanisms, i.e. in termolecular reactions as a third body species with high collisional efficiency or directly participating in bimolecular reactions. [ABSTRACT FROM AUTHOR]

A lab scale fuel processor test prototype (FPP) was designed, constructed, and used in analyzing steady state performance of individual propane oxidative steam reforming (OSR) reactor and serially combined propane OSR and water gas shift (WGS) reactors. OSR and WGS reactions were performed over novel Pt‐Ni/δ-Al 2 O 3 and Au‐Re/ZrO 2 catalysts, respectively. During the steady state tests, concentrations of C 3 H 8 , O 2 , H 2 , CH 4 , CO and CO 2 in the feed and product streams were measured on line-real time by a mass spectrometer. The tests have been conducted for different compositions of oxygen, propane and steam in the feed stream of OSR reactor in both individual and serial tests. The highest achieved H 2 /CO product ratio was ca. 32–33 for 723–623 K and 673–573 K OSR-WGS reactor temperature combinations in serial operation, with S/C feed ratio of 3 and O/C feed ratio of 0.74. In the performance tests, maximum conversions achieved were 100% C 3 H 8 and 50% CO in the OSR and WGS reactors, respectively. In the tests, steady state, dry basis, inert free, H 2 concentrations higher than 50% and CO concentrations as low as 1% in the WGS product stream were obtained. The performance stability of both catalysts were confirmed by the product concentration profiles obtained during 75 h time-on-stream stability test performed on OSR-WGS system and by microstructural characterization of the OSR and WGS catalysts as well. [ABSTRACT FROM AUTHOR]

The kinetics of propane oxidation over Pt/Al 2 O 3 are investigated in this work as a function of O 2 /C 3 H 8 ratio in the 150–300 °C temperature range. At high O 2 /C 3 H 8 ratios, the platinum nanoparticles are saturated with oxygen and the reaction rate is zero-order with respect to the oxygen partial pressures in this regime. As the oxygen coverage decreases with decreasing O 2 /C 3 H 8 ratio, the reaction rate increases and the reaction order changes from zero-order to negative-order in the oxygen partial pressure. The reaction rate is controlled to a large extent by the oxygen coverage on the platinum nanoparticles. However, at lower temperatures and higher oxygen pressures there is a slow deactivation of the catalyst that cannot be explained by a slow change in the oxygen coverage. Diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) of adsorbed CO was performed to track the evolution of the nanoparticle structure over the course of the propane oxidation reaction and to determine whether the slow deactivation was caused by reconstruction of the platinum nanoparticles. We found that the platinum nanoparticles are significantly reconstructed during the course of the reaction, including the formation of a platinum oxide (PtO) which has a characteristic CO-DRIFTS band at 2123 cm −1 . The extent of PtO formation decreases with increasing temperature and, as a result, deactivation of the catalyst is less severe at higher temperatures. Unexpectedly, increasing the oxygen partial pressure resulted in less PtO formation. We believe that a different platinum oxide phase (e.g. PtO 2 or Pt 3 O 4 ) is formed at higher oxygen pressures, which is reduced to metallic platinum during CO exposure at 25 °C, and therefore is not detectable by CO-DRIFTS. These results are unique because they show how the nanoparticle structure evolves over many hours of propane oxidation, and how the temperature and oxygen pressure influence the reconstruction of the nanoparticles, which has implications for a wide range of reactions not limited to propane oxidation. [ABSTRACT FROM AUTHOR]

SBA-15 supported Mo oxide catalysts (Mo/SBA) were prepared and the local structures of the Mo species were investigated by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) measurements. The local structure of Mo on Mo/SBA was able to be controlled from T d monomer to O h oligomer by increasing the Mo loading. The selectivity of propane photo-oxidation reaction was dependent on the local structure of Mo species. [ABSTRACT FROM AUTHOR]

Hydrogen production using the partial oxidation of propane over supported metal catalysts was studied in a small isothermal packed-bed reactor. Ceria was used as the support, due to its ability to store and release oxygen, with nickel and platinum being the metals used. The overall purpose of the study was to determine the pathways and sequences of hydrogen production. Flow rates of the inlet stream were varied from 100 to 400 scc/min, and two weights of each catalyst were used. The reactions were carried out at 600 °C and 1 atm, with a ratio of O 2 to C 3 H 8 maintained at 1.78. For the experimentally observed products leaving the reactor, the corresponding reaction matrix was subjected to Gauss elimination to determine that four independent reactions could be obtained. This results in a maximum of ten sets of these reactions. The number of sets was reduced by carrying out a material balance on the products to determine the net rate of each of the four reactions; sets containing negative rates for irreversible reactions could then be eliminated from consideration. To determine the validity of any remaining sets containing dry-reforming, steam-reforming and water-gas shift reactions, a secondary set of experiments were carried out at the outlet conditions of the original experiments to see if those three reactions could indeed take place. Eventually, only one set of four reactions was deemed suitable for the Pt/CeO 2 catalyst, incorporating total oxidation, partial oxidation, dehydrogenation and water formation. The extents of these four reactions were followed as a function of contact time, showing that partial oxidation decreases down the reactor, while total oxidation increases. For the Ni/CeO 2 catalyst, three sets were suitable. The three are very similar, in that they all contain total oxidation, steam reforming and dehydrogenation, with the fourth reaction being partial oxidation, dry reforming or water formation. Qualitatively, the same results are found for all three sets. Total oxidation is the predominant reaction at all contact times, with steam reforming and/or dry reforming producing hydrogen only at larger contact times. The differences between the results for the two supported catalysts indicate that different types of reactors should be chosen, depending upon the catalyst to be used. For supported nickel catalysts, large packed-bed reactors may be optimal, while micro-reactors in parallel may be best for supported platinum catalysts. [ABSTRACT FROM AUTHOR]

Ru-Re/γ-AlO catalysts were prepared by two sequential impregnation methods and their performances for the total oxidation of propane were investigated. TEM, XRD and H chemisorption data showed that the metal particle size was about 1.8 nm on both bimetallic catalysts. However, compared to the Ru/γ-AlO catalyst with dispersion of 0.52, the Ru dispersion was improved by the presence of Re going from 0.64 for the catalyst with Re deposited on Ru/γ-AlO, to 0.70 for the sample with Ru deposited on Re/γ-AlO. The O adsorption data indicated that in the Re-modified catalysts the subsurface oxidation of Ru was suppressed, while in the Ru/γ-AlO catalyst ruthenium was oxidized to a larger extent under oxidizing conditions at room temperature. The Ru deposited on Re/γ-AlO exhibited a catalytic performance slightly better than the catalyst with Re impregnated on Ru/γ-AlO, but activity of Re-modified catalysts was not improved as compared to the Ru/γ-AlO catalyst. On the other hand, bimetallic Ru-Re/γ-AlO catalysts present better online stability and no deactivation was observed after the on-line tests for 30 h at temperature of 220 °C. TEM and XRD data showed that oxidized rhenium species strongly interacted with γ-alumina prevented large agglomeration of the Ru phase under O-rich reaction conditions. The used monometallic Ru catalyst contained RuO oxide with crystallite size of 26 nm, while in the used bimetallic catalysts with size of 6-7 nm. Thus, in the consecutive catalytic tests Re-promoted Ru/γ-AlO catalysts present higher activity and extended resistance to deactivation. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Low temperature propane oxidation has been achieved by Co 3 O 4 -based nano-array catalysts featuring low catalytic materials loading (15 mg under flow rate of 150 mL/min). The increased Ni doping into the Co 3 O 4 lattice has led to 100% propane conversion at low temperature (<400 °C) and has enhanced reaction kinetics by promoting the surface lattice oxygen activity. In situ DRIFTS investigations in tandem with isotopic oxygen exchange reveals that the propane oxidation proceeds via a Mars-van Krevelen mechanism where surface lattice oxygen acts as the active site whereas O 2 in the reaction feed does not directly participate in CO 2 formation. The Ni doping promotes the formation of less stable carbonates on the surface to facilitate the CO 2 desorption. The thermal stability of Ni doped Co 3 O 4 decreases with increased Ni concentration despite the increased catalytic activity. A balance between enhanced activity and compromised thermal stability is considered in the Ni doped Co 3 O 4 nano-array catalysts for hydrocarbon oxidation. This study provides useful and timely guidance for rational catalyst design toward low temperature catalytic oxidation. [ABSTRACT FROM AUTHOR]

A hydrothermal strategy combined with colloidal deposition synthesis was successfully used to grow ZnO/perovskite (LaBO 3 , B = Mn, Co, Ni) core–shell nanorod arrays within three dimensional (3-D) honeycomb cordierite substrates. A facile sonication assisted colloidal wash coating process is able to coat a uniformly dispersed perovskite nanoparticles onto the large scale ZnO nanorod arrays rooted on the channel surfaces of the 3D cordierite substrate achieved by hydrothermal synthesis. Compared to traditional wash-coated perovskite catalysts, an enhanced catalytic performance was observed for propane oxidation with 25 °C lower light-off temperature than powder-form coated perovskite catalyst of similar LaMnO 3 loading (4.3 mg). Temperature programmed reduction and desorption under H 2 and O 2 atmosphere, respectively, were used to study the reducibility and oxygen activity of these core–shell nanorod array based monolithic catalysts, revealing a catalytic activity sequence of LaCoO 3 > LaMnO 3 > La 2 NiO 4 at the initial stage of catalytic reaction. The good dispersion and size control in La-based perovskite nanoparticles and their interfaces to ZnO nanorod array support may contribute to the enhancement of catalytic performance. This work may provide a new type of Pt-group metals (PGM) free catalysts with improved catalytic performance for hydrocarbon oxidations at low temperature. [ABSTRACT FROM AUTHOR]

Catalytic activity of nano-Au-catalyst(s) for the complete propane oxidation was investigated. The results showed that the nature of both Au precursor and support strongly influences catalytic activity of the Au-catalyst(s) for the propane oxidation. Oxidation state, size, and dispersion of Au nanoparticles in the Au-catalysts, surface area, crystallinity, phase structure, and redox property of the support are the key aspects for the complete propane oxidation. Among the studied Au-catalysts, the AuHAuCl4-Ce catalyst is found to be the most active catalyst. [ABSTRACT FROM AUTHOR]

We used density functional theory quantum mechanics with periodic boundary conditions to determine the atomistic mechanism underlying catalytic activation of propane by the Ml phase of Mo-V-Nb-Te-0 mixed metal oxides. We find that propane is activated by Te--O through our recently established reduction-coupled oxo activation mechanism. More importantly, we find that the C -H activation activity of Te = 0 is controlled by the distribution of nearby V atoms, leading to a range of activation barriers from 34 to 23 kcal/mol. On the basis of the new insight into this mechanism, we propose a synthesis strategy that we expect to form a much more selective single-phase Mo-V-Nb-Te-0 catalyst. [ABSTRACT FROM AUTHOR]

Differently prepared vanadium promoted Pt/alumina catalysts have been prepared, characterized and tested for propane total oxidation. V-promoted Pt/Al 2 O 3 catalysts have shown remarkably higher catalytic activity than V-free Pt/Al 2 O 3 catalyst. Among V-promoted Pt catalysts that prepared by coimpregnation gave the highest alkane conversions in the whole range of reaction temperatures studied. Factors such as Pt particle size or the oxidation state of platinum do not seem to be the responsible for the enhanced performance. Modification of the redox properties of the catalyst (i.e. high reducibility of vanadium species) likely provoked by the close contact between platinum particles and vanadium species and the partial introduction of vanadium in the platinum particles can be related to the improved reactivity of the PtV catalysts. [ABSTRACT FROM AUTHOR]