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Abstract: The objective of this work was to gain a better understanding of the influence of Sn on the dispersion of Pt in platinum supported SBA-15 catalysts and thereby on the dehydrogenation of propane (DHP) activity, selectivity to propylene, coking and catalyst stability. To this end, DHP over Pt-SBA-15 and Pt-Sn-SBA-15, prepared by incipient wetness impregnation (IW), was studied at 793K by means of tapered element oscillating microbalance (TEOM) coupled with on-line gas-chromatography. This allowed us to determine simultaneously the comprehensive information from a single catalysis experiment. The catalysts were characterised by N2-physisorption, transmission electron microscopy (TEM-EDXS), X-ray diffraction (XRD) and H2-chemisorption, which revealed that the presence of Sn results in higher Pt dispersion by the formation of Pt–Sn alloy. It is evident from TEOM studies that after 220min on stream the amount of coke formed is almost three times higher over Pt-Sn-SBA-15-IW than on its counterpart Pt-SBA-15-IW, albeit the former exhibits considerably higher propane conversion, superior selectivity to propylene and stability than the latter. It is demonstrated that propane conversion and coke formation on the catalysts can be correlated with Pt particle size. A modified drain-off effect is proposed to explain the superior selectivity and stability of the bimetallic than the monometallic catalyst. [Copyright &y& Elsevier]

Abstract: Studies on dehydrogenation of propane (DHP) over monometallic Pt-SBA-15 catalysts, which contain markedly different Pt particle sizes, reveal that the reaction is dependent on the size of the particle. Catalyst with smaller particles (∼3nm) is much more active and less selective than that with larger particles (∼21nm). Rate of coking, selectivity to coke formation and the amount of coke formed are significantly higher over the former than that on the latter. [Copyright &y& Elsevier]

Abstract: Cu/CNF and Cu/CeO2/CNF catalysts have been synthesized and characterized on different nanostructured carbon nanofibers (CNF). The samples have been tested in isopropanol dehydrogenation. Cu/CNF show similar activity to Cu catalysts supported on activated carbon. Cu/CeO2 nanotubes have been synthesized on the CNF surfaces. The Cu/CeO2 nanotubes exhibit much higher activity and lower activation energy than Cu/CNF. The selectivity towards acetone depends on the fraction of CeO2 in the composites. High activity and selectivity has been achieved with a Cu12Ce5/CNF catalyst. [Copyright &y& Elsevier]

First-principles calculations have been performed to investigate CH4 dissociation and C diffusion during the Ni/Fe-catalyzed growth of carbon nanofibers (CNFs). Two bulk models with different Ni to Fe molar ratios (1:1 and 2:1) are constructed, and x-ray diffraction (XRD) simulations are conducted to evaluate their reliability. With the comparison between the calculated and experimental XRD patterns, these models are found to be well suited to reproduce the crystalline structures of Ni/Fe bulk alloys. The calculations indicate the binding of the C1 derivatives to the Ni/Fe closest-packed surfaces is strengthened compared to that on Ni(111), arising from the upshift of the weighted d-band centers of catalyst surfaces. Then, the transition states for the four successive dehydrogenation steps in CH4 dissociation are located using the dimer method. It is found that the energy barriers for the first three steps are rather close on the alloyed Ni/Fe and Ni surfaces, while the activation energy for CH dissociation is substantially lowered with the introduction of Fe. The dissolution of the generated C from the surface into the bulk of the Ni/Fe alloys is thermodynamically favorable, and the diffusion of C through catalyst particles is hindered by the Fe component. With the combination of density functional theory calculations and kinetic analysis, the C concentration in catalyst particles is predicted to increase with the Fe content. Meanwhile, other experimental conditions, such as the composition of carbon-containing gases, feedstock partial pressure, and reaction temperature, are also found to play a key role in determining the C concentration in bulk metal, and hence the microstructures of generated CNFs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Non-precious intermetallic compound catalysts for propane dehydrogenation. • Scaling relations are established using formation energies over terraces and steps. • Descriptor-based microkinetic analysis is carried out to obtain volcano curves. • Fe 3 Ga 1 is a good catalyst candidate with improved catalytic performance. By using a descriptor-based microkinetic analysis combined with results from density functional theory calculations over eight transition-metal (including Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) terrace and stepped surfaces, intermetallic compounds have been screened to search for inexpensive and environmentally friendly propane dehydrogenation (PDH) catalysts with enhanced catalytic performance. Based on the scaling relations, the formation energies of ethyl on terrace and methylidyne on stepped surfaces are identified as two descriptors to represent the energetics of other reaction intermediates and transition sates. The derived PDH activity and propylene selectivity volcano curves not only provide a rational interpretation of the previously experimentally reported catalyst candidates, but also predict several unexpected binary combinations by screening 1482 A 3 B 1 and 741 A 1 B 1 intermetallic compounds. The non-precious Fe 3 Ga 1 is then synthesized and evaluated. Its improved propylene selectivity and catalytic stability with respect to those of the Pt catalyst validates the theoretical predictions experimentally. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: The catalytic properties of the CeO2 catalyst for propane dehydrogenation (PDH) are examined by employing the density functional theory calculations. Surface modifications and their effects on the surface reactivity are explored by creating the oxygen vacancy and single Pt atom doping. A comparative study between the binding energies of the different PDH reaction species reveals a considerable Lewis acid‐base interaction over the pristine and defective surfaces, which dominantly strengthens the bond formation between the adsorbates and the catalyst surface, resulting in the enhancement of surface reactivity. The creation of oxygen vacancy and doping the CeO2(111) surface with single Pt atoms changes the charge distribution over the surface on account of excess 4f electrons. This electronic change increases the bond formation abilities of the inactive Ce atom and hence increases the adsorption strength. Oxygen vacancy in the defective CeO2(111) surface migrates over the surface with the addition of an appropriate adsorbate. Moreover, it is revealed that the propylene is more strongly adsorbed on the single‐Pt‐atom‐doped CeO2(111) surface than the pristine and defective surfaces, which decreases the deep dehydrogenation energy barrier and ultimately results in the lowering of the selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • The electronic structure of V 2 O 3 upon single-atom doping is examined. • A weak Lewis acid-base interaction is found to occur on the pristine surface. • The first dehydrogenation step is identified as the rate-limiting step for PDH. • Mn 1 -V 2 O 3 is suggested to be a good catalyst candidate for PDH. Vanadium-oxide-based catalysts have recently been found very promising for the catalytic dehydrogenation of propane. In this work, self-consistent density functional theory calculations have been performed to examine how the electronic structure of the V 2 O 3 (0001) surface is modified by single-atom doping and how the catalytic properties can be tailored to propane dehydrogenation. The structural stability of single-atom-doped V 2 O 3 (0001) surfaces is assessed by comparing the adsorption energies of single atoms with the cohesive energies of bulk metals. A weak Lewis acid-base interaction is found to occur on the pristine surface, which can be strengthened and weakened by substitution of single atoms for V and O, respectively. On these two types of oxide surfaces, single atoms act as promoters and active sites. The first dehydrogenation step is identified as the rate-limiting step by microkinetic analysis. On all the single-atom-doped surfaces, the activation energy for water formation is higher than that for hydrogen recombination, implying that reduction of the oxide surfaces is difficult to take place during the course of the reaction. If a compromise between the catalytic activity and catalyst selectivity is made, Mn 1 -V 2 O 3 is suggested to be a good candidate as the catalyst for propane dehydrogenation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atomically dispersed Pt-rTiO 2 catalyst shows good catalytic performance for PDH. • Single and dual Pt atoms can be tightly held by vacancies created on reduced TiO 2. • Dual-Pt-atom structure is the active ensemble for the C H bond activation. Tailoring atomically dispersed catalysts by various methods has been the subject of intense current research in heterogeneous catalysis. In this work, the structural stability and propane dehydrogenation performance of Pt-TiO 2 catalysts with single, dual, and triple Pt atoms doped on the reduced TiO 2 surface have been examined. Experimental results indicate the atomically dispersed Pt is thermally very stable and shows exceptionally high activity (TOF propane = 4.93 s−1) and selectivity (∼98.5 %) for the dehydrogenation reaction. The recently developed machine-learning-based SSW-NN method is then employed to explore the global potential energy surface of the atomically dispersed Pt atom-doped TiO 2 , which suggests that the single and dual Pt atoms can be tightly held by the vacancies created on the reduced transition-metal oxide, as confirmed by DFT + U calculated energetics. After that, advanced characterization techniques are used in conjunction with microkinetic analysis to establish the quantitative structure–activity relationships. It is found that the dual-Pt-atom structure with two Pt atoms embedded in adjacent Ti and O vacancies is the only active ensemble that dramatically promotes the C H bond activation and hydrogen recombination, as compared to single Pt atoms accommodated by either Ti or O vacancies. These results provide new and direct evidence in support of the idea that specific function can be imparted to specific active sites by tuning their coordination environments, which makes it possible to tailor the catalytic properties of metal oxides to a particular reaction such as propane dehydrogenation. [ABSTRACT FROM AUTHOR]

Abstract: A highly efficient sp3–sp3 carbon–carbon bond formation system was developed for the aerobic ruthenium-catalyzed oxidative cross-dehydrogenative coupling reaction between tertiary amines and sp3 C–H compounds in the presence of RuCl3/O2, thus giving the corresponding α-functionalized amines. Compared with the reported method, H2O2 or t BuOOH was replaced successfully by economical and facile oxygen as the oxidant. Three types of activated C–H bonds for pronucleophiles were evaluated in this system. All these features combined are in accordance with important prospective green chemistry aspects. [Copyright &y& Elsevier]

Abstract: The influence of the pore geometry of the catalyst supports on dehydrogenation of propane (DHP) activity, selectivity to propylene and the degree of coke formation was evaluated over micro-(Pt-ZSM-5 and Pt-Beta) and meso-(Pt-SBA-15) porous materials in a tapered element oscillating microbalance (TEOM) reactor by analyzing reaction products and mass changes simultaneously. The catalysts were prepared by incipient wetness impregnation and were characterized by N2-physisorption, X-ray diffraction (XRD) and H2-chemisorption. The characterization results indicate that catalysts contain Pt within the pores and Pt nanoparticles of more or less similar sizes however stabilized on markedly different pore geometries (structure and size). This allowed to (i) largely marginalize the effect of the sizes of Pt particles on DHP and (ii) evaluate exclusively the vital role of pore geometry of the supports, where a fraction of Pt is located within the pores, on the catalytic performance. Pt-ZSM-5 presents the highest propane conversion followed by Pt-Beta and Pt-SBA-15 indicating that the activity decreases with increasing pore size (ZSM-5

Abstract: Carbon nanofibers (CNFs) with different microstructures were synthesized as the support of Pt catalyst for decalin dehydrogenation to evolve pure hydrogen. The results show that in a liquid-film state at the temperature of 240°C for reactor external heating, 5wt% Pt catalyst supported on platelet CNFs gives a TOF of 732.4mol H2/mol metal in 2h. The microstructure of CNFs and the metal particle size have great impact on the performance of the catalyst for the reaction. [Copyright &y& Elsevier]

• CH 4 direct dehydrogenation is preferred on Ni. • OH-assisted dehydrogenation of CH 4 is favored on Pt and Ni@Pt. • CO 2 direct dissociation is more favorable than H-assisted way on Ni. • H-assisted CO 2 dissociation is the dominant way on Pt and Ni@Pt. CO 2 reforming of methane (DRM) is a promising reaction for the carbon cycle in nature. Ni was found to be active in this process. However, single component Ni catalysts cannot meet the stability, activity and selectivity demands simultaneously. This paper presents a systematical density functional theory study to investigate the catalytic performance of Ni@Pt(1 1 1) core-shell surface compared with Ni(1 1 1) and Pt(1 1 1) in methane dry reforming. Two ways of O* and OH* assisted CH 4 dehydrogenation are considered in present work. CH 4 direct dissociation is more favored on Ni, while OH*-assisted CH 4 dehydrogenation is more competitive to proceed on Pt and Ni@Pt compared with direct way. Furthermore, Ni@Pt provides much less energy-demanding pathways for both CH and C oxidation, under the assistance of O* or OH*. Therefore, CH is much easier to be oxidized rather than decomposition into carbon on this surface, meanwhile, it is beneficial for carbon elimination and shows promising anti-carbon formation performance. Finally, free energy profiles are plotted at 1000 K and dominant reaction mechanisms of DRM conditions are proposed on three surfaces, respectively. On Ni(1 1 1), O* generated from CO 2 direct dissociation could provide dominant oxidant for CH* oxidation, while on Pt(1 1 1) and Ni@Pt, OH* originated from CO 2 H-assisted dissociation acted as the major oxidant for CH* oxidation. This work sheds some light on dominant reaction pathway and surface carbon formation, which could provide new mechanistic insight into CO 2 reforming methane on Ni-core/Pt-shell surface. [ABSTRACT FROM AUTHOR]

Abstract: A strategy is presented for making metal clusters encapsulated inside microporous solids selectively accessible to reactant molecules by manipulating molecular sieve size and affinity for adsorbed molecules. This expands the catalytic capabilities of these materials to reactions demanding high selectivity and stability. Selective hydrogen combustion was achieved over Pt clusters encapsulated in LTA zeolite (KA, NaA, CaA) in a propene‐rich mixture obtained from propane dehydrogenation, showing pore‐size dependent selectivity and coking rate. Propene tended to adsorb at channels or external surfaces of zeolite, interfering the diffusion of hydrogen and oxygen. Tailoring the surface of LTA zeolite with additional alkali or alkaline earth oxides contributed to narrowing zeolite pore size and their affinity for propene. The thus‐modified Pt@KA catalyst displayed excellent hydrogen combustion selectivity (98.5 %) with high activity and superior anti‐coking and anti‐sintering properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Substitution of transition metals for Cr increases the acidity of the adjacent O. • Linear scaling relations are established to identify the PDH activity descriptor. • High propylene selectivity of the M 1 -Cr 2 O 3 catalysts is achieved. • Cu 1 -Cr 2 O 3 is predicted to be the best catalyst for PDH among the 13 doped Cr 2 O 3. The catalytic behavior of M 1 -Cr 2 O 3 (M = Mn-Cu, Ru-Ag, and Os-Au) in propane dehydrogenation (PDH) has been studied by employing microkinetic modeling combined with results from periodic DFT + U calculations. Calculated results indicate that most of the single atoms concerned can be stably present on the Cr 2 O 3 surface. The adsorption energy calculations and Bader charge analysis demonstrate that the acidity of the O sites adjacent to the M sites would be enhanced upon doping, which in turn strengthens the atomic H adsorption and the co-adsorption of various PDH species. The surface H formation energy is identified as the reactivity descriptor for PDH over the M 1 -Cr 2 O 3 catalysts, and a volcano curve of the PDH activity is obtained. By calculating the difference between the propylene dehydrogenation and desorption barriers, it is found that some M 1 -Cr 2 O 3 catalysts show improved selectivity towards propylene, as compared to Cr 2 O 3. Comparison between the formation barriers of H 2 and H 2 O reveals that single-atom doping has no apparent negative effect on the catalytic stability of the Cr 2 O 3 surface. The Cu 1 -Cr 2 O 3 catalyst is finally identified as the most promising catalyst for PDH among the 13 M 1 -Cr 2 O 3 catalyst candidates, considering the catalytic activity, selectivity, stability, and cost. [ABSTRACT FROM AUTHOR]

To investigate the role of steam on the structure and activities of platinum-based catalyst, a tin modified Pt/γ-Al 2 O 3 catalyst was prepared for propane dehydrogenation in the presence of steam. The propane conversion could be prominently elevated by nearly twofolds with only 1.0% loss of selectivity to propene when an optimum amount of H 2 O was added. The retarding effects of steam on the activities are also observed at higher H 2 O/C 3 H 8 molar ratios (>1). Kinetic studies results show that the apparent activation energies for steam dehydrogenations are lower than those without steam addition. The fresh, spent and steam pretreated catalysts were characterized by TG, Raman, H 2 -chem, HAADF-STEM, XPS and CO adsorption FT-IR (CO-FTIR). It is observed that the platinum particles sizes are smaller in the samples subjected to certain period of steam pretreatment. The changes of platinum dispersion in steam conditions are related to the changes of tin oxidation states and the segregation of platinum from Pt–Sn alloys, as revealed by CO-FTIR and XPS results. More accessible Pt sites that are generated in the steam due to the phase transformation of Pt–Sn catalyst as well as the removal of coke accumulated on the catalyst surface would account for the increase of catalytic activities and the decrease of activation energies in steam atmosphere. Competitive adsorption of H 2 O and other reagent over Pt sites would lead to the retarding effects of steam on the activities at high H 2 O partial pressure. [ABSTRACT FROM AUTHOR]

Abstract: Ni catalysts are widely used to catalyze ammonia decomposition. In this study, first-principles calculations are performed to investigate the preferred adsorption sites and the adsorption energies of NHx (x=0–3) and H, and the transition states, activation energies and rate constants of NH3 stepwise dehydrogenation and associative desorption of N on the stepped Ni(211) and the close-packed Ni(111) surfaces. The results show that the barrier of associative desorption of N, which is higher than those of NH3 stepwise dehydrogenation, on Ni(211) are 1.10eV higher than that on Ni(111), indicating that the associative desorption of N on Ni(211) is difficult to take place. Hence the strongly adsorbed N atoms would block some of the step sites of Ni(211). The N-blocking Ni(211) surface is constructed, and then NH3 decomposition on 2N–Ni(211) is investigated. The results indicate that Ni catalysts with too many or too few step sites, which can be associated with Ni particle sizes, show low ammonia decomposition activities. Therefore, different sized Ni-based catalysts are employed to catalyze ammonia decomposition, and TOFH2 as a function of Ni particle size is correlated. Finally, the structure sensitivity of ammonia decomposition over Ni catalysts is rationally interpreted. [Copyright &y& Elsevier]

Abstract: First-principles calculations based on density functional theory (DFT) have been performed to study the adsorption and decomposition of NH3 on Ni(110). The adsorption sites, the adsorption energies, the transition states and the activation energies of the stepwise dehydrogenation of NH3 and the associative desorption of N are determined, and the zero point energy correction is included, which makes it possible to compute the rate constants of the elementary steps in NH3 decomposition. Combined DFT calculations and kinetic analysis at 350K indicate that the associative desorption of N has a reaction rate lower than NHx dehydrogenation and is therefore the rate determining step. The distinctly different rate constants over Ni(110), Ni(111) and Ni(211) imply that ammonia decomposition over Ni-based catalyst is a structure-sensitive reaction. [Copyright &y& Elsevier]

The influences of gas compositions on the rates of coke formation over a Pt-Sn/AlO catalyst are studied. The coke formed on the catalyst is characterized by thermal gravimetric analysis, IR spectroscopy, Raman spectroscopy and elemental analysis. Two kinds of coke are identified from the TPO profiles and assigned to the coke on the metal and the coke on the support, respectively. The coke formed on the metal is softer (containing more hydrogen) than that formed on the support. The rate of coke formation on the metal is weakly dependent on the propylene and hydrogen pressures but increasing with the propane pressure, while the rate of coke formation on the support is increasing with the propane and propylene pressures and decreasing with the hydrogen pressure. Based on the kinetic analysis, a mechanism for the coke formation on the Pt-Sn/AlO catalyst is proposed, and the dimerization of adsorbed CH is identified to be the kinetic relevant step for coke formation on the metal. [ABSTRACT FROM AUTHOR]

Abstract: First-principles calculations based on density functional theory have been performed to elucidate the reaction mechanism for ethylbenzene dehydrogenation and the role of CO2 in H removal. On the basis of the experimental information and theoretical prediction, three model surfaces with Fe-, ferryl- and O-termination are constructed to represent the active Fe2O3(0001) surface. The calculated results indicate that on all of the three surfaces the C–H activation in the methylene group followed by the dehydrogenation of the methyl group is kinetically more favorable. The energy barriers for ethylbenzene dehydrogenation are lowest on the O-terminated surface, but the generated styrene is adsorbed too strongly to be released. As CO2 decomposition and the formation of HCOO are hindered by the relatively high activation energies, CO2 cannot serve as the oxidant to recover the O- and ferryl-terminated surfaces to keep the redox cycle. At the steady state of the reaction the coupling mechanism dominates on the Fe-terminated surface, with the synergistic effect between ethylbenzene dehydrogenation and the reverse water–gas shift reaction. Since the energy barrier for the formation of COOH is comparable to that for H2 formation, both the one-step and two-step pathways are predicted to contribute to the coupling mechanism, although the former is more probable. [Copyright &y& Elsevier]

Abstract: Langmuir–Hinshelwood kinetic models for catalytic propane dehydrogenation on Pt -Sn/Al2O3 are proposed based on the reaction mechanisms that take into account the one step or two-step dehydrogenation and are evaluated by fitting the experiments. When taking into consideration the fitting accuracy, the number of fitting parameters and the rigorousness of the reaction mechanism, the kinetics of propane dehydrogenation based on the assumptions of step-wise dehydrogenation, the first step dehydrogenation as the rate-determining step, and low surface coverage of C3H7 outperforms other kinetic models. The change of catalyst activity with time-on-stream is related to the rate of coke formation that depends on the partial pressures of propene and hydrogen. Finally a complete kinetic model, which includes propane dehydrogenation and cracking and catalyst deactivation because of coking, is developed, which is found to agree well with the changes of propane conversions with time-on-stream under different operating conditions. Direct measurement of coke formation is avoided by the approach employed in this study for the prediction of catalyst deactivation by coke deposition. [Copyright &y& Elsevier]

Abstract: A HCHO reduction method was used to prepare Pt/CNF catalysts for decalin dehydrogenation to produce pure hydrogen. The effects of pH adjustment, Pt loading and especially reduction temperature were discussed based on zeta potential and metal particle size measurement and XPS and TPR characterization. It was shown that the efficiency of Pt loading was significantly enhanced by adjusting the pH and the activity of the Pt/CNF catalyst was consequently improved. Higher Pt loading did not lead to better catalyst activity because of the growth of Pt particles. Increasing the reduction temperature promoted the reduction of Pt species but not changed the particle size. Complete reduction of the Pt catalyst was preferred to increase the catalyst activity. Excellent activity and selectivity were observed for the catalyst reduced at 80°C with a real Pt loading of 5.40wt.%, yielding 729.9mol H2/mol Pt in 2h. [ABSTRACT FROM AUTHOR]

Abstract: Dehydrogenation of propane (DHP) was studied over a series of xCr–SBA-15 and xCr–Al2O3 catalysts, prepared by incipient wetness impregnation, to gain a better understanding of the nature and distribution of Cr species and their catalytic function. To this end, the catalysts were characterized by N2-physisorption, X-ray diffraction (XRD), UV-Raman spectroscopy, scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM–EDXS) and X-ray absorption spectroscopy (XANES and EXAFS). All these characterization techniques indicate that, at ⩽1 wt% Cr, SBA-15 contains exclusively uniform distribution of chromium as isolated Cr(VI) species in tetrahedral () coordination, whilst on γ-Al2O3 a fraction of oligomers (including dimers) is present along with isolated species. At ⩾5 wt% Cr, SBA-15 is dominated by crystalline α-Cr2O3 particles, besides a fraction of isolated Cr(VI) species in coordination. Remarkably, γ-Al2O3 contains mainly oligomers with different degrees of nuclearity and a fraction of isolated species but no Cr2O3 particles. Among xCr–SBA-15 catalysts, those containing exclusively isolated Cr species (i.e., ⩽1 wt% Cr) exhibit higher activity and selectivity with respect to per mole of Cr than the catalyst dominated by crystalline α-Cr2O3 particles (⩾5 wt% Cr). The intrinsic activity of these isolated Cr species is higher than those observed on γ-Al2O3 (⩽1 wt% Cr). Interestingly, among xCr–Al2O3, the catalysts dominated by oligomeric species show the highest activity, indicating the important role of the species in the reaction. In situ XAS studies evidence that active Cr sites are apparently generated on-site during the reaction and that Cr is typically in (III) oxidation state. Based on ex situ and in situ characterization results and catalytic data, it appears that the activity of the Cr species is different in xCr–SBA-15 and xCr–Al2O3. For xCr–SBA-15, isolated Cr(III) sites with coordination number greater than four are more active, selective and stable than Cr sites on the surface of crystalline Cr2O3. In contrast, for xCr–Al2O3, oligomeric Cr species are more active and selective than the isolated Cr sites. [Copyright &y& Elsevier]

Abstract: The rational design of the carbon nanofiber catalysts for oxidative dehydrogenation of ethylbenzene (ODE) has been discussed based on a reviewed reaction mechanism. The synthesized carbon nanofibers with systematically varied graphitic platelet orientations have been used as a model system for the rational catalyst design, in respect to the carbon nanofiber properties such as the amount of basic groups, the crystallinity, and the ratio between the prismatic area and the basal plane area. Well defined carbon nanofibers have been synthesized by hydrocarbon or carbon monoxide decomposition on the sub-iron group catalysts and at selected preparation conditions. The catalytic test in a fixed bed reactor at a temperature of 400°C shows that the stable activity and selectivity can be obtained on the well-defined carbon nanofibers catalysts. Removing the residual metal in carbon nanofibers does not evidently influence the catalytic behavior whereas the lower conversion of ethylbenzene can be observed on the high-temperature treated carbon nanofiber samples. No clear evidences are found for the catalytic behavior being related to the surface area and graphitization degree of carbon nanofibers. The basic oxygen-containing groups are identified as the active sites by TPD–MS and a special method suggested by Boehm. The ratio between the prismatic surface area and the basal area has been identified as the most important parameter for the rational catalyst design. The fish-bone catalysts CNF 20 seems to be the best catalyst in the samples studied in the present work, due to the large number of basic edge groups, the optimum ratio between the prismatic and basal plane area. It can result in a delicate balance in the redox catalytic cycle. As a consequence, the formation of CO2 can be reduced. [Copyright &y& Elsevier]

• Pt/MgAl 2 O 4 shows robust dehydrogenation activity being twice that of Pt/CNF. • Edge Pt sites are discriminated to be the dominant active sites. • Partial positively charged Pt prevents the strong adsorption of products on catalyst. Platinum group metals hold pronounced potential for the dehydrogenation process of liquid organic hydrogen carriers (LOHCs) such as decalin, but the strong adsorption of dehydrogenation product has suppressed the moving forward of these catalysts. Herein, we described that the strong interactions between Pt and MgAl 2 O 4 trigger partial positively charged Pt, which mitigates the adsorption of naphthalene on highly active Pt sites, thus achieving an outstanding decalin dehydrogenation activity that is nearly twice that of state-of-the-art Pt/CNF catalysts. As revealed by various characterization outcomes and DFT calculations, the strong electronic interactions between Pt and spinel oxygen surface resulted in partial positively charged Pt on MgAl 2 O 4 , which inhibits the electron transfer from Pt to unsaturated carbon of naphthalene, thus weakening the bond strength between Pt and naphthalene. As a result, the combination of small-sized Pt nanoparticles and facile desorption of products endows tremendous dehydrogenation activity of Pt/MgAl 2 O 4. This study may shed new light on the rational construction of highly efficient metal catalysts for the application of LOHCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The performances of VO x /Al 2 O 3 can be tuned by changing the alumina calcination temperature. • The intrinsic activity of VO x /θ-Al 2 O 3 is two times higher than that of VO x /γ-Al 2 O 3. • The enhanced reducibility and weakened VO x -support interaction contribute to activity enhancements. • The coking behavior of VO x /Al 2 O 3 depends both on total surface acid sites and VO x polymerization degree. Supported vanadium oxides are promising in propane non-oxidative dehydrogenation and the activity of which shows clear support effects. The present study reports the effects of alumina polymorphs on the structure and performances of VO x -based catalysts. VO x /Al 2 O 3 catalysts with the same V surface density were prepared over four different alumina supports (γ-Al 2 O 3 , δ-Al 2 O 3 , θ-Al 2 O 3 , θ,α-Al 2 O 3) obtained by varying the calcination temperature of boehmite. The alumina calcination temperature was shown to affect the surface acid properties and VO x -support interactions and make it possible to tune the activity and coking behavior of catalysts. Weakening the VO x -support interactions due to the change in alumina surface properties was found critical to improve the intrinsic activity of catalysts. The coking behavior of catalysts was shown to depend on both total acid sites and VO x polymerization degree. This study may provide basic principles to tune the performance of VO x -based catalysts for non-oxidative dehydrogenation. [ABSTRACT FROM AUTHOR]

• High selectivity of core-shell alloy catalysts for propane dehydrogenation. • Linear scaling relations are established to identify the descriptor. • Microkinetic modeling is carried out to obtain turnover frequency. • Co@Pt is the best catalyst by making a compromise between activity and selectivity. Microkinetic analysis combined with the results obtained from density functional theory calculations has been performed to examine the catalytic activity and selectivity of Pt-based core-shell alloy catalysts for propane dehydrogenation. Calculated results indicate that substitution of 11 late transition metals for the core region of Pt nanoparticles would significantly modify the electronic structure of the surface Pt atoms through the strain effect and charge transfer. The core-shell catalysts are found to have less negative propylene adsorption energies and higher activation energies for the dehydrogenation reactions than Pt, thus giving rise to a lower catalytic activity and a higher selectivity toward propylene. Linear chemisorption energy and transition state energy scaling relations hold very well in the present work, and the adsorption energy of propylene is identified to be a good descriptor to represent the overall kinetics. The scaling relations also suggest that a higher catalyst selectivity toward propylene can only be achieved at the expense of a lower catalytic activity for propane dehydrogenation. If a compromise is made between catalytic activity and catalyst selectivity, Co@Pt is proposed to be the best core-shell catalyst for propane dehydrogenation. [ABSTRACT FROM AUTHOR]