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Abstract: The phenol steam reforming reaction toward H2 formation has been investigated in the 575–730 °C range over MgO, CeO2, and ZrO2 single metal oxides and various mixed metal oxides such as Mg–Ce–O, Mg–Zr–O, and Mg–Ce–Zr–O, all prepared by the sol–gel method. The same reaction has also been studied over Rh supported on these metal oxides. The effects of synthesis method of the Mg–Ce–Zr–O support (mechanical mixing versus sol–gel) and of Rh deposition (wet impregnation versus sol–gel) on the activity and H2 selectivity of the reaction over the Rh/Mg–Ce–Zr–O catalyst have also been investigated. It was found that 0.5 wt% Rh/MgO and 0.1 wt% Rh/Mg–Ce–Zr–O catalysts, the supports of which were prepared by the sol–gel method, exhibit better performance when compared to a commercial Ni-based catalyst used for tar steam reforming. In particular, Rh/MgO presented the highest H2 product concentrations and selectivities in the 575–730 °C range and no more than 20% drop in activity after 24 h of continuous reaction (0.5% C6H5OH/40% H2O/He). It was found that steam reforming of phenol is favored over very small Rh particles in the case of 0.1 wt% Rh/Mg–Ce–Zr–O catalyst. In particular, the specific integral reaction rate of H2 production (mmol-H2 / (m2 Rh s)) significantly increased by decreasing the Rh particle size from 2.7 to 1.2 nm. The effect of the partial pressure of water and phenol in the feed stream on catalyst activity was found to strongly depend on support chemical composition. More than one kind of carbonaceous species forming during reaction has been identified with varying compositions and reactivities toward oxygen and steam. XPS studies suggested that the Mg x Zr1−x O2 phase present in the Mg–Ce–Zr–O support is reduced by H2 at 300 °C in the presence of very small Rh particles leading to the creation of oxygen vacant sites and diffusion of Zr toward the bulk of the crystal. As a result of this, the surface acidity and basicity of the Rh/Mg–Ce–Zr–O catalyst are expected to alter, thus influencing the hydrogen activity and selectivity of the reaction. [Copyright &y& Elsevier]

Abstract: The effect of the presence of varying titanium concentrations introduced into hexagonal mesoporous silica (HMS) support on the catalytic activity of the catalysts was evaluated in the hydrodesulfurization of 4-ethyl-6-methyl dibenzothiophene (4E6MDBT) in a fixed-bed reactor at , , and WHSV=46.4 h−1. The catalysts were characterized by , XRD, DRS, FTIR spectroscopy of the framework vibration, DRIFTS in the OH region, , FT-IR spectroscopy of adsorbed NO and pyridine, XPS, and TGA. All Ti-containing catalysts showed higher activity than the Ti-free CoMo/HMS sample. The catalyst with a Si/Ti molar ratio of 40 is the most active. The HDS of 4E6MDBT over the Ti-free catalyst proceeds mainly via the dealkylation (DA) route, and then HDS of the more reactive DBT occurs. After Ti-incorporation into the HMS material, additional acid-catalyzed isomerization occurs, followed by direct HDS and HYD. Based on the catalyst activity–structure correlation, the increase in HDS activity over the Ti-containing catalysts with respect to the Ti-free sample was attributed to increased CoS2 and MoS2 surface exposure, as well as increased Lewis and Brønsted acidity. [Copyright &y& Elsevier]

Abstract: A series of titanium–silica catalysts was prepared by grafting a titanium isopropoxide precursor on amorphous silica substrates with BET areas of 162–709 m2 g−1 and pore volumes of 0.5–1.4 mL g−1. The grafting process, consisting of hydrolysis of the Ti precursor by the hydroxyl groups of the silica surface, yielded catalysts containing Ti loadings of 0.65–2.37 wt%. The textural properties of the Ti/SiO2 catalysts were evaluated from the nitrogen adsorption–desorption isotherms, and their surface species were studied by ultraviolet–visible (UV–vis) spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS) techniques. These catalysts were tested in the liquid phase epoxidation of oct-1-ene with hydrogen peroxide as a model reaction. All catalysts showed very high (95–98%) hydrogen peroxide consumption at 353 K after 1 h reaction time, but selectivity to the epoxide was strongly dependent on the pore volume of the silica substrate. Under these reaction conditions, an epoxide selectivity as high as 90–93% was reached on the catalysts with the largest pore volumes (1.4 mL g−1). Spectroscopic techniques also revealed that TiIV ions coordinated tetrahedrally by oxide ions are essential to obtaining highly selective catalysts in the reaction. [Copyright &y& Elsevier]

The catalytic properties of the V2O5/ZrO2 system for the oxidative dehydrogenation of propane were studied. Catalysts with different chemical compositions (i.e., vanadium oxide loadings) were prepared, with activation done by calcination at two temperature levels. Samples were characterized by nitrogen adsorption, temperature-programmed reduction, and Raman and photoelectron spectroscopic techniques. It was found that calcination temperature level strongly affects the structure of ZrO2 (tetragonal zirconia predominates at 500 °C while the transformation to a monoclinic phase occurs at 650 °C). The calcination temperature also affects the nature of vanadium oxide species on the surface of ZrO2. After calcination at 500 °C surface vanadium oxide species are formed at low vanadium loadings, but crystalline V2O5 structures appear at the higher ones. Calcination at 650 °C leads to the formation of ZrV2O7, mainly at high vanadium loadings. The results of propane oxidative dehydrogenation show that surface-isolated vanadium oxide species are more selective to C3H6. On the other hand, it was found that the catalysts suffer a slow deactivation during reaction due to ZrV2O7 formation. This transformation decreases the activity but the activity-selectivity profile is not affected. [Copyright &y& Elsevier]

A series of titanium-silica catalysts with relatively low Ti contents were prepared by dispersing titanium isopropoxide in a solvent (cyclohexanol, 1-phenylethanol, 1-hexanol, 2-(2-ethoxyethoxy)ethanol, diglyme, and acetophenone) and then mixing each solution with the silica substrate. The process consisting of the hydrolysis of the Ti precursor by the hydroxyl groups of the silica surface yielded catalysts containing Ti loadings of 0.8–3.0 wt%. The catalysts prepared were characterized using various spectroscopic techniques, including diffuse reflectance infrared Fourier transform (DRIFTS), ultraviolet–visible (UV–vis), and photoelectron (XPS) spectroscopic techniques. The catalytic activity of the catalysts studied was determined using liquid-phase epoxidation of 1-octene with hydrogen peroxide as a model reaction. All catalysts showed very high hydrogen peroxide consumption but the selectivity to the epoxide was seen to be strongly dependent upon the solvent used in the preparation. Only the catalyst prepared using cyclohexanol solvent, in which the titanium content was low (0.8 wt%) and the Ti(IV) ions were isolated tetrahedrally coordinated by oxide anions, exhibited very high (95%) selectivity to the epoxide. The other Ti/SiO2 catalysts containing a higher amount of titanium (1.0–3.0 wt%), but less disperse and with Ti(IV) in an octahedral environment, exhibited poor performance in the target reaction. [Copyright &y& Elsevier]

• Pd doped Co mesoporous SiO 2 core@shell nanocatalyst were prepared. • The incorporation of Pd can effectively increase the catalytic activity. • Hydrodechlorination by-products were not formed for an optimal Pd-Co composition. • The optimal Pd-Co composition catalyst was reused for 5 cycles with high selectivity and moderate activity. This study describes the synthesis of palladium-promoted Co@SiO 2 catalyst developed by electrostatic immobilization of Pd ionic precursor onto Co 3 O 4 nanoparticles core, coated with a mesoporous SiO 2 shell. The oxidized Pd-Co 3 O 4 @SiO 2 (xPdCo-ox) and partially reduced Pd-Co@SiO 2 (xPdCo-red) nanocatalysts were used in the direct synthesis of chloro-arylamines from chloronitroarenes employing heterogeneous hydrogenation process. The effect of palladium content (xPdCo; x = 0.0, 0.5, 1.0 and 3.0 Pd wt%) in the Co 3 O 4 core of the structures on catalytic performance for the hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN) was systematically studied. It was found that the incorporation of palladium ionic precursor promotes both Co 3 O 4 core nanoparticles flocculation and an increase in the mesoporous shell thickness in the Pd-promoted catalysts compared to the pristine Co-SiO 2 core-shell structure. The TPR, XRD, XPS and magnetic measurements results indicated that the palladium addition promoted the reduction of Co 3 O 4 core during the isothermal H 2 treatment at 873 K rendering metallic Pd° and Co° species. The catalytic CNB hydrogenation experiments showed that the 0.5PdCo-red catalyst inhibited both the hydrodechlorination and intermediates accumulation reaching 99% yield in CAN compared to 1.0PdCo-red and 3.0PdCo-red catalysts which provided aniline as undesired product. Additionally, the 0.5PdCo-red catalyst was easily recycled with a moderate catalytic activity after five consecutive reaction cycles. Finally, the catalytic hydrogenation performance of the 0.5PdCo-red catalyst for different pharmaceutical substituted chloro-nitroarenes such as 1-(4-chlorophenoxy)-2-nitrobenzene, 2-chloro-1-((3-fluorobenzyl)oxy)-4-nitrobenzene and 2-chloro-5nitrobenzotrifluoride was also evaluated and revealed high activity (>99% at 3 h of reaction) and selectivity towards the desired chloro-arylmines production, highlighting the potential of this catalyst in these processes. [ABSTRACT FROM AUTHOR]

An alumina-supported vanadium oxide catalyst (13.9 wt.% vanadium oxide) has been characterized by different techniques and tested in the gas phase oxidation of furfural. These studies have shown that the catalyst unavoidably deactivates by deposition of maleates and resins over the surface. Full regeneration is accomplished by burning off these deposits at 773 K. The studies have also demonstrated that if the primary contact occurs at temperatures at which furfural conversion is low and then the temperature is increased in a low- to high-temperature mode, intense deposition of maleates and resins takes place and the catalyst is rapidly deactivated. The increase of the temperature does not result in removal of deposits but accelerates the deposition. Under this protocol, the yield of maleic anhydride never exceeded 30%, irrespective of the reaction conditions (temperature and O 2 /furfural mole ratio). In contrast, if the catalyst first contacts the reaction mixture at high oxidizing potential, then the rate of maleate and resin deposition is much slower, and so is the deactivation rate, and the catalyst can display a higher yield of maleic anhydride for a longer period of time. A high oxidizing potential can be attained at a high reaction temperature (close to full conversion). A higher oxidizing potential at a given high temperature can be accomplished by increasing the O 2 /furfural mole ratio. Thus, for example, first contacting the catalyst at 593 K (full conversion), 1 vol.% of furfural, and O 2 /furfural mole ratio = 10, obtained an initial maleic anhydride yield of 68%, and the yield was still greater than 50% after 15 h on stream. On contacting at 573 K with 1 vol.% furfural and 20 vol.% O 2 , the maleic anhydride yield was initially close to 75% and was above 60% after 15 h. [ABSTRACT FROM AUTHOR]

The effect on the geometric, electronic, and catalytic properties of LaMnO 3 oxides of replacement of 50% Mn with Cr, Fe, Co, and Ni in combustion reactions of dimethyl ether has been studied. The similarity in the ionic radius does not produce larger differences in the geometric properties of the compounds, whereas the differences in the stability of their cation valences produce significant changes in their electronic properties. The high stability of Cr 3+ and Fe 3+ species does not increase the Mn 4+ /Mn 3+ redox pair ratio in LaMn 0.5 Cr 0.5 O 3 and LaMn 0.5 Fe 0.5 O 3 . Meanwhile, the high stability of Co 2+ and Ni 2+ species favors the oxidation of Mn 3+ to Mn 4+ and the mobility of anionic oxygen in the LaMn 0.5 Co 0.5 O 3 and LaMn 0.5 Ni 0.5 O 3 catalysts, which improves their catalytic performance. [ABSTRACT FROM AUTHOR]

The synthesis of anatase TiO 2 nanoparticles with controlled morphology and increased {001} facets exposed without the presence of fluorine-derived substances is a challenge. Herein, we report a highly effective approach to fabricate anatase TiO 2 nanoplates with exposed {001} facets and their exploitation as robust photocatalytic materials for dye remediation. These materials were synthesized under controlled hydrolysis and condensation reactions, using titanium (IV) n -butoxide in an ethanolic solution, with acetic and sulfuric acids, by a solvothermal method at 190 °C with or without the presence of the non-ionic surfactant Triton® X-100 and then characterized. During TiO 2 crystal synthesis, the effect of a non-ionic surfactant on the TiO 2 particle growth was investigated. Our results demonstrate that the proposed method can synthesize pure and crystalline anatase TiO 2 square nanoplates that form nanostructured spheres with high surface area, uniformly sized mesopores, and exposed {001} facets. The presence of non-ionic surfactant increased the exposed {001} facets percentage of the formed nanoplates from 69 to 80%, decreased the crystallite thickness, but unaffected its crystalline phase and band gap energy. The kinetic constants (K a e K b) for the synthesized TiO 2 anatase nanoplates are considerably higher than the commercial TiO 2 anatase constant (K c). The synthesized photocatalysts show higher efficiency in the photocatalytic removal of methylene blue (MB) than commercial TiO 2 (for t = 120 min). [Display omitted] • Anatase TiO 2 nanoplates as robust photocatalytic materials for methylene blue remediation. • The influence of non-ionic surfactant on the synthesis of anatase TiO 2 nanoplates was considered. • Kinetic constants for synthesized TiO 2 anatase nanoplates are higher than for commercial. • Higher efficiency in photocatalytic removal of methylene blue than commercial TiO 2. [ABSTRACT FROM AUTHOR]

Abstract: Molybdenum carbide has been prepared according to the carbothermal reduction method. Carbon black substrate was used as C-source whereas a H2-flow was the reducing agent. Two different H2 consumption steps were identified during the carburization treatment. The low temperature step is related to the reduction of Mo6+-to-Mo4+, the higher temperature process accounts for the deep reduction of Mo4+-to-metal Mo0 and its subsequent reaction with C to form the Mo-carbide. The influences of the maximum carburization temperature, carburization time, gas hourly space velocity regarding Mo-loading, heating rate and temperature of Ar pre-treatment were analyzed. All these conditions are interrelated to each other. Thus, the carburization process ends at 700°C when Mo-loading is 10wt%, however Mo-loading higher than 10wt% requires higher temperatures. Carburization temperatures up to 800°C are needed to fulfill Mo-carbide formation with samples containing 50wt% Mo. Nevertheless, Ar pre-treatment at 550°C and slow heating rates favor the carburization, thus requiring lower carburization temperatures to reach the same carburization level. [Copyright &y& Elsevier]

The combustion of coal can result in trace elements, such as mercury, being released from power stations with potentially harmful effects for both human health and the environment. Research is ongoing to develop cost-effective and efficient control technologies for mercury removal from coal-fired power plants, the largest source of anthropogenic mercury emissions. A number of activated carbon sorbents have been demonstrated to be effective for mercury retention in coal combustion power plants. However, more economic alternatives need to be developed. Raw biomass gasification chars could serve as low-cost sorbents for capturing mercury since they are sub-products generated during a thermal conversion process. The aim of this study was to evaluate different biomass gasification chars as mercury sorbents in a simulated coal combustion flue gas. The results were compared with those obtained using a commercial activated carbon. Chars from a mixture of paper and plastic waste showed the highest retention capacity. It was found that not only a high carbon content and a well developed microporosity but also a high chlorine content and a high aluminium content improved the mercury retention capacity of biomass gasification chars. No relationship could be inferred between the surface oxygen functional groups and mercury retention in the char samples evaluated. [Copyright &y& Elsevier]

Abstract: Mesoporous metallosilicates (HMS–M; M=Ce, Fe, Ti) were used as supports for the preparation of Au catalysts, and were tested in the liquid-phase hydrogenation of biphenyl at 5MPa and 488K. Irrespective of the support, uniformly dispersed Au nanoparticles in range 3.2–6.5nm were obtained. The highest turn over frequency (TOF), expressed per surface Au atom, was achieved on the Au/HMS–Fe, furthermore this catalyst gave the highest selectivity to the most saturated compound (bicyclohexyl with the highest cetane number) by means of enhancing the second aromatic-ring hydrogenation. From the catalyst activity-structure correlation, the highest activity of the Au/HMS–Fe catalyst is linked with: (i) the higher ratio of positively charged metallic gold Au δ+/Si (XPS), and (ii) the higher stability of Au nanoparticles (HRTEM). A linear correlation between the activity (per gram of metal) of the catalysts and their ratio Au δ+/Si is observed; however, Au/HMS–Ce catalyst displays a different behaviour in terms of activity per gram of metal exposed caused by the fact that ceria is not incorporated in the framework. [Copyright &y& Elsevier]

Abstract: Raman spectroscopy is used to evidence both the nature of the interphase reaction between ZnO and MnO2 particles and its kinetic evolution. Zn cations migrate from the ZnO grains during oxygen vacancies formation process and diffuse into the MnO2 particles leading to an interphase region with an intermediate valence Mn+3–O–Mn+4. Large amounts of desorbed Zn cations promote the formation of ZnMn2O4 structure, in addition to the intermediate valence state. The system evolves towards complete formation of the spinel phase at higher thermal treatment times. The reactivity of the ZnO plays an important role in the formation of this interphase. Low-reactivity ZnO powder, in which the oxygen vacancies are previously produced, shows a stabilization of the intermediate valence state with very limited formation of the spinel phase. A clear correlation between the amount of the intermediate state interphase and the magnetic properties has been established. [Copyright &y& Elsevier]

Abstract: A study is presented of the kinetics and oxidation selectivity of methyl-ethyl-ketone (MEK) in air over bimetallic PdO x (0–1 wt% Pd)–MnO x (18 wt% Mn)/Al2O3 and monometallic PdO x (1 wt% Pd)/Al2O3 and MnO x (18 wt% Mn)/Al2O3 catalysts. Reaction rate data were obtained at temperatures in the 443–523 K range and for MEK partial pressures in the reactor feed of between 6.5 and 126.6 Pa. Products of both MEK combustion and partial oxidation reactions were found. Monometallic Pd/Al2O3 was the most selective catalyst for complete oxidation whereas the partial oxidation of MEK in the presence of manganese oxides was significant. The maximum yield for the partial oxidation products (acetaldehyde, methyl-vinyl-ketone, and diacetyl) was always below 10%. Kinetic studies showed that the rates of CO2 formation over PdO x /Al2O3 were well-fitted by the surface redox Mars–van Krevelen (MvK) kinetic expression and also by a Langmuir–Hinshelwood (LH) model derived after considering the surface reaction between adsorbed MEK and oxygen as the rate-determining step. In the case of the Mn-containing catalysts the MvK model provides the best fit. Irrespective of the model, the kinetic parameters for the bimetallic Pd–Mn catalysts were between the values obtained for the monometallic samples, suggesting an additive rather than a cooperative effect between palladium and manganese species for MEK combustion. [Copyright &y& Elsevier]

This paper focuses on the effect of Ru and Rh addition to SiO2-supported Co catalysts for the oxidative steam reforming of ethanol to produce hydrogen. Catalysts were tested in the reaction at atmospheric pressure and 623–673 K and characterized by X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, and infrared spectroscopy with CO as the probe molecule. A synergistic effect between Co and Rh or Ru was seen in the oxidative steam reforming of ethanol. A study of the deactivation/regeneration of catalysts found that an oxidizing treatment recovered the performance of deactivated bimetallic catalysts. This process could be used in cycles to optimize both ethanol conversion and selectivity toward hydrogen production. [Copyright &y& Elsevier]

Calcium was added to CeZrO4 mixed oxide by wet impregnation with a Ca nitrate solution to achieve solids with nominal Ca/(Ce+Zr) atomic ratios of 0.01, 0.02, 0.05, 0.1, 0.2, and 0.5. The solids were calcined at 873 K to decompose the Ca nitrate to CaO. The determination of oxygen storage capacity complete (OSCC) and FTIR studies of the formation of surface superoxide radicals (O− 2) were conducted to study the oxygen storage and release (OSR) properties of the solids. Both measurements indicate that the OSR properties clearly deteriorated for samples with nominal Ca/(Ce+Zr) at. ratios >0.01 (0.9 atoms of Ca nm−2). The degree of deactivation increased with increasing Ca loading; for the sample with the largest Ca loading, the OSCC was ca. 3-fold lower than that of bare CeZrO4. The solids also were characterized by TGA, chemical analysis by TXRF, XRD, N2 isotherms, and XPS. The results indicate that the Ca remained on the surface of the CeZrO4 as supported CaO; the formation of large bulky crystals of CeZrCa mixed oxides by solid-state reaction between the Ca phase and the CeZrO4 did not occur. For Ca loading below the amount required to completely cover the surface (which, experimentally, is ca. 18 atoms of Ca per nm2 of surface), CaO existed as very well-dispersed CaO domains few atoms thick. Above this value, the surface was completely covered by CaO, and three-dimensional crystals of CaO were formed. Given these results, we propose that the main mechanism for the deterioration of OSR properties of CeZrO4 by incorporation of CaO on the surface by impregnation is fouling: CaO physically prevents contact between the O2 gas and the surface sites of the CeZrO4. It also is likely that a very limited solid-state reaction occurs between the latter two phases, with a CaZrO3-like amorphous oxide formed at the grain boundaries. The formation of this amorphous oxide also can chemically contribute to the deactivation. The relevance of these results in the understanding of the deactivation of TWC by Ca is discussed. [Copyright &y& Elsevier]

Abstract: LaFeO3, LaNiO3 and substituted LaFe1− y Ni y O3 (y=0.1, 0.2 and 0.3) perovskites were synthesized by the citrate method and used in the catalytic combustion of ethanol and acetyl acetate. Chemical composition was determined by atomic absorption spectrometry (AAS) and specific areas from nitrogen adsorption isotherms. Structural details and surface properties were evaluated by temperature-programmed reduction (TPR), infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), temperature-programmed desorption of oxygen (O2-TPD) and photoelectron spectroscopy (XPS). Characterization data revealed that total insertion of nickel in the LaFeO3 takes place for substitution y=0.1. However, NiO segregation occurs to some extent, specifically at higher substitutions (y>0.1). The catalytic performance of these perovskites was evaluated in the combustion of acetyl acetate and ethanol. Among these molecules, ethanol exhibited the lowest ignition temperature, and the catalytic activity expressed as intrinsic activity (molm−2 h−1) was found to increase substantially with the nickel substitution. These results can be explained in terms of the cooperative effect of a LaFe1− y Ni y O3 and NiO phases, whose relative concentration determines the oxygen activation capability and hence their reactivity. [Copyright &y& Elsevier]

Abstract: The catalytic oxidation of methane was investigated over six catalysts with different palladium and platinum molar ratios. The catalysts were characterised by TEM, EDS, XPS, PXRD and temperature-programmed oxidation. The results suggest that in the bimetallic catalysts, an alloy between Pd and Pt was formed in close contact with the PdO phase, with an exception for the Pt-rich catalyst, where no PdO was observed. It was found that the molar ratio between palladium and platinum clearly influences both the activity and the stability of methane conversion. By adding small amounts of platinum into the palladium catalyst, improved activity was obtained in comparison with the monometallic palladium catalyst. However, higher amounts of platinum are required for stabilising the methane conversion. The most promising catalysts with respect to both activity and stability were Pd67Pt33 and Pd50Pt50. The platinum-rich catalyst showed very poor activity for methane conversion. [Copyright &y& Elsevier]

Abstract: Supported Fe catalysts of varying support chemical composition prepared by sol–gel and incipient wetness impregnation methods were studied for the steam reforming of phenol (one of the main constituents of tar produced during steam gasification of wood biomass) in the 600–700 °C range. Various natural CO2 absorbent materials were also used together with the supported Fe catalyst in a fixed-bed microreactor to investigate the enhancement of H2 production during short times on stream, as well as the removal of CO2 from the reaction product gas (absorption enhanced reforming [AER]). A 5 wt% Fe/50Mg-50Ce-O catalyst was found to be the most active in terms of H2 product yield, with one of the lowest amounts of accumulated carbonaceous deposits. Among a series of Fe/50Mg-50Ce-O () catalysts, H2-specific integral production rate (mol-H2/(g s)) goes through a maximum at the 5 wt% Fe loading, whereas the largest amount of “carbon” deposits was measured on the highest Fe-loaded (10 wt%) catalyst. The stability of the 5 wt% Fe/50Mg-50Ce-O catalyst was studied during consecutive oxidation→reaction and oxidation→reduction→reaction cycles of short duration. X-Ray diffraction, X-ray photoelectron spectroscopy, and Mössbauer studies were performed for detailed physicochemical characterization of the supported Fe catalysts in their fresh and used states (after phenol steam reforming). The most active Fe-based catalyst (5 wt% Fe/50Mg-50Ce-O) was found to present a high Fe2+/Fe3+ ratio after phenol steam reforming (Mössbauer studies). Various transient experiments demonstrated that the enhanced production of H2 occurring in the presence of a CO2 absorbent material (supported Fe+CO2 absorbent) for short times on stream was due to a change in the water–gas shift reaction (CO+H2O↔CO2 +H2) toward further H2 production. The 5 wt% Fe/Mg-Ce-O catalyst was found to compete favorably with a 35 wt% Ni/γ-Al2O3 industrial catalyst (used for tar steam reforming) at 700 °C in terms of H2 product yield and to have significantly lower CO/CO2 product ratios. [Copyright &y& Elsevier]

Abstract: A zirconium-doped mesoporous silica (MSU) was used as a support for Co, CoMo, and CoW catalysts with varying Mo and W loadings. Their activity was tested in the hydrogenation and hydrogenolysis/hydrocracking of tetralin under varying temperatures, experimental conditions, and concentrations of dibenzothiophene (DBT) in a high-pressure, fixed-bed, continuous-flow stainless steel catalytic reactor operating at a pressure of 6.0 MPa. Textural, structural, and metallic properties were studied by XRD, XPS, H2-TPR, NH3-TPD, and N2 adsorption–desorption isotherms. The results indicate that the addition of a promoter, such as W and Mo, improves their catalytic properties in hydrogenation reactions with or without DBT in the feed compared with catalysts containing only cobalt as an active phase. The hydrogenation yield is higher in the case of molybdenum- and tungsten-promoted catalysts, but the molybdenum-promoted catalysts enhances the yield most significantly; with a catalyst containing 5 wt% of Mo at 315 °C with a contact time of 3.6 s and an H2:tetralin molar ratio of 15, the hydrogenation yield is 93.5%, whereas a catalyst containing 15 wt% of Co gives a yield of 74.0%. The yield of hydrogenolysis/hydrocracking is lower for the promoted catalysts, although those containing tungsten exhibit an intermediate behavior between those containing only cobalt or cobalt and molybdenum as active phases. However, catalysts with molybdenum as a promoter agent have very good thiotolerant properties. With 15 wt% of cobalt and 5 wt% of molybdenum, when 850 ppm of DBT is added to the feed, the conversion of tetralin is nearly 52.0% with a 44.0% yield of hydrogenation products after 6 h on stream; for a catalyst with 15% of cobalt, these values are only 13.1 and 0.9%, respectively, after 5 h on stream. [Copyright &y& Elsevier]

Abstract: The chemical nature of P-containing species incorporated on the surface and within the subsurface regions of CeO2 solid and their effects on the deterioration of the oxygen storage and release properties of phosphated ceria have been investigated. The samples were characterised by X-ray diffraction, X-ray photoelectron, Raman, and 31P nuclear magnetic resonance spectroscopies; Fourier transform infrared pyridine chemisorption, N2 physical adsorption isotherms, oxygen storage capacity, and 18O2 temperature-programmed isotopic exchange measurements. In the samples with P/Ce ratios <0.03, isolated orthophosphate species are present on the surface and in the subsurface regions of CeO2 solid. In these samples, deterioration of the oxygen storage and release properties correlates very well with the amount of P incorporated as isolated orthophosphates, because oxygen diffusion within the subsurface region of CeO2 is increasingly inhibited. These results show that the presence of CePO4 (monazite) is not essential for the deterioration of oxygen storage and release properties in CeO2. In the samples with P/Ce>0.03, crystals of monazite are formed. Theoretical estimations indicate that about 5.5 P atoms/nm2 are required to fully cover the CeO2 surface. This is equivalent to a P/Ce ratio of 0.02 in the ceria solid studied in the present work (BET area=12.8 m2/g). The experimental P/Ce ratio needed for complete surface saturation is higher (close to 0.03) very likely because part of P is incorporated into the subsurface region of ceria. Monazite also deteriorates the oxygen storage and release properties of ceria because it is a very stable Ce(III) phase. Once CePO4 crystals are formed, further incorporation of P does not result in a deeper deterioration of the oxygen storage and release properties of ceria. Larger monazite crystals are then formed on the surface at the expense of isolated orthophosphate species, leaving part of the ceria surface uncovered and thus available for surface and bulk oxygen exchange. [Copyright &y& Elsevier]

Abstract: Fe–Ce mixed oxides prepared by coprecipitation showed considerable synergy in N2O decomposition when compared with pure metal oxide counterparts. The mixed system also displayed higher stability in reaction at high temperature. Through characterisation by XRD, XPS and TPR, the activity–stability improvement is ascribed to the formation of Fe-doped ceria and Ce-doped hematite and also to increased surface area. The intimate interaction in the mixed phases results in easier reduction. Thus the release of oxygen, which is the rate-determining step in this N2O decomposition, becomes more facile. [Copyright &y& Elsevier]

Abstract: The efficiency of Fe–Mn–Zn–Ti–O mixed-metal oxides of varying composition prepared by sol–gel methods toward removal of H2S from a gas mixture containing 0.06 vol% H2S, 25 vol% H2, 7.5 vol% CO2, and 1–3 vol% H2O was studied in the 25–100 °C range. In particular, the effects of the Fe/Mn molar ratio in the Fe–Mn–Zn–Ti–O solids on the H2S uptake and regeneration performance of the solids were studied. The nominal chemical composition (metal mol%) of the Fe–Mn–Zn–Ti–O solids was found to strongly influence the chemical composition, particle size, and morphology of the crystal phases formed. It was found that the 5 Fe–15 Mn–40 Zn–40 Ti–O mixed-metal oxide provides the highest H2S uptake as fresh and after regeneration in 20% O2/He gas mixture in the 500–750 °C range compared with the other solids investigated. It was also found that 5 Fe–15 Mn–40 Zn–40 Ti–O exhibits higher H2S uptake than a commercial Ni-based H2S adsorbent in the 25–50 °C range. In particular, a three times greater H2S uptake at 25 °C compared with that on the commercial adsorbent was found. The effectiveness of the regeneration procedure of 5 Fe–15 Mn–40 Zn–40 Ti–O solid after complete sulfidation was found to be in the 48–82% range, depending on the sulfidation temperature and regeneration conditions applied. A detailed characterization of the fresh, sulfided, and regenerated 5 Fe–15 Mn–40 Zn–40 Ti–O and 20 Fe– 40 Zn–40 Ti–O solids, which exhibited the best and worst H2S uptake performance, respectively, using BET, XRD, Raman, XPS, and Mössbauer techniques revealed important information on the sulfidation mechanism. The present work provides new fundamental knowledge that could trigger further research efforts toward the development of alternative mixed metal oxides not based on toxic chromia (Cr2O3–Fe2O3/α-Al2O3), which is used today in several industrial plants for the catalytic oxidation of H2S (Claus process). [Copyright &y& Elsevier]

Abstract: The effects of the preparation method (combustion and incipient wetness) and Co loading (1–5 wt%) on the structure, redox, and morphological properties of the Co/CeO2 system were probed by X-ray diffraction, X-ray photoemission spectroscopy, scanning electron microscopy, CO and H2 chemisorption and temperature-programmed desorption measurements. Synthesis route and Co-loading control the structure and morphological properties, markedly affecting the reactivity of the Co/CeO2 system in the Fischer–Tropsch synthesis (FTS) reaction (; ). Both metal–support interaction(s) and Co dispersion control the strength and relative concentration of CO and H2 adsorption sites enabling marked differences in the specific site–time–yield of the various catalysts. [Copyright &y& Elsevier]

Abstract: A novel catalyst was prepared by sulphation of vanadium supported on carbon-coated monoliths with a mixture of SO2 +O2 at 473 K. The as-sulphated catalyst shows about twofold higher conversion than the fresh catalyst in the selective catalytic reduction of NO at low temperatures () after an induction period. The increase in activity during the induction period is correlated with the buildup of more stable sulphate species. The sulphated catalyst was characterised by temperature-programmed desorption, photoelectron spectroscopy, temperature-programmed reaction, and transient response techniques. We have found evidence indicating that sulphates are anchored to carbon in the vicinity of vanadyl sites. This fact can account for the improvement of the redox properties in the sulphated catalyst. On the basis of experimental results, the enhancement of the redox properties, rather than the increase in acidity, is the cause of the superior performance of the sulphated catalyst compared with the fresh one. [Copyright &y& Elsevier]

In an attempt to gain fundamental information about the role of P on the chemical deactivation of a three-way catalyst (TWC), P was deliberatively incorporated in CeO2 and Ce0.8Zr0.2O2 solid solution. XRD, Raman, XPS, and N2 physisorption studies have indicated that monazite, a Ce(III) phosphate (CePO4) solid phase, is located at the surface/subsurface region of both solids. Different experimental approaches were used to investigate the alteration by P incorporation of the redox chemistry of CeO2 and Ce0.8Zr0.2O2 solids that is relevant to the oxygen storage and release properties of the current commercial TWCs. In particular, H2-TPR, dynamic OSC measurements using CO and H2 pulses, 18O2 temperature-programmed isotopic exchange (TPIE), and 18O2 transient isothermal isotopic exchange have been used. These studies revealed that the amount of labile surface and bulk oxygen and the bulk oxygen diffusion rates are significantly reduced when the solids are contaminated with phosphorus. The monazite present in the surface and subsurface region of the solid is proposed to be responsible for these results. The reduction of Ce(IV) present in the CeO2 and Ce0.8Zr0.2O2 solids is also affected. Ce(III) in monazite is very stable and cannot be oxidized to Ce(IV). Therefore, it cannot participate in the redox Ce(IV)/Ce(III) couple needed for the reduction of Ce(IV). Moreover, the formation of bulk and surface O vacant sites needed for the O storage and release steps involved in the OSC process was also found to be affected. The results of the present work provide support to the hypothesis that formation of monazite is one of the main chemical deactivation mechanisms of real TWCs since CePO4 was found in deactivated vehicle-aged TWCs. [Copyright &y& Elsevier]

A combination of in situ Raman, XANES, and EPR spectroscopies is used to study the nature of the interaction between V and Ce in the ceria-supported vanadia catalysts. Vanadium oxide species disperse on ceria up to 9 V atoms/nm2 of support. Surface V5+ species closely interacts with ceria support promoting a reduction of surface Ce4+ to Ce3+. Upon heating or during reaction surface vanadia reacts with ceria support forming a CeVO4 phase. The active site appears to be V5+&z.sbnd;O&z.sbnd;Ce3+ for both systems. The redox cycle for oxidative dehydrogenation appears to be associated with Ce, rather than with V sites. [Copyright &y& Elsevier]

Molybdophosphoric (HPMo) and tungstophosphoric (HPW) acid catalysts, supported on hexagonal mesoporous silica (HMS) carriers and modified with Ti, Zr, and Zr + Al, were prepared. The catalysts were characterized by Fourier transform IR spectroscopy of adsorbed pyridine and deuterated acetonitrile, X-ray photoelectron spectroscopy, and 31P and 1H nuclear magnetic resonance. Catalytic activity was tested in the hydrodesulfurization reaction of DBT. The thermal stability and the properties of the supported molybdophosphates and tungstophosphates were discussed in terms of support effect. For the hydrodesulfurization reaction, which was carried out under high hydrogen pressure, the HPMo/ZrAlHMS catalyst had higher activity and selectivity to biphenyl formation than the other supported HPMo catalysts. Regardless of the carrier, supported HPW catalysts were the most active. [Copyright &y& Elsevier]

Production of H2 from methanol by steam reforming, partial oxidation, or a combination thereof was studied over Cu/ZnO-based catalysts. The catalysts were characterized by a variety of techniques, including N2O chemisorption, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature-programmed reduction/oxidation. The influence of feed composition, reaction temperature, and catalyst formulation on H2 production rate, product distribution, and catalyst lifetime was investigated. Distinct differences between the processes were observed with respect to catalyst behavior. ZrO2-containing catalysts, especially Cu/ZnO/ZrO2/Al2O3, exhibit the best performance in the steam reforming reaction. During partial oxidation, however, a binary Cu/ZnO catalyst exhibits the lowest light-off temperature and the lowest level of CO by-product. The redox properties of the catalyst appear to play a key role in determining the pathway for H2 production. In particular, the extent of methanol and/or H2 combustion at differential O2 conversion is strongly dependent on the ease of copper oxidation in the catalyst. [Copyright &y& Elsevier]

Bimetallic PtSn/γ-Al2O3–La2O3 catalysts were prepared by two comparative methods, successive impregnation (SI) and controlled surface reaction (CSR). FTIR-pyridine adsorption revealed a decrease in support acidity as a function of lanthanum content. Oxidized Pt2+ was identified by CO-FTIR chemisorption and by XPS spectra on catalysts prepared by SI. When the CSR preparation method was used, reduced Pt0 was observed and oxidized Pt2+ was not detected. As the lanthanum content increased a diminution in cyclohexane dehydrogenation and n-heptane conversion was observed. Low hydrogenolysis and high selectivity to C7-olefins were obtained in both preparations. It is proposed that lanthanum in SI catalysts stabilizes the platinum in an oxidation state, Pt2+, and diminishes the support acidity. In CSR preparations the lanthanum effect is limited to inhibit the support acidity and hence to the bifunctional reactions occurring during the n-heptane conversion. [Copyright &y& Elsevier]

A thorough characterization of CoZSM5 and PtCoZSM5 before and after catalytic use was carried out using a battery of techniques. The bimetallic solid was more selective for N2 production. The TPR profiles showed significant differences. No solid, either fresh or used, exhibited any of the characteristic cobalt oxide X-ray reflections. The XPS data provided information concerning cobalt dispersion. The Raman spectroscopy clearly indicated that Co3O4 species were present only in the monometallic zeolites while a form of highly dispersed CoxOy moieties became dominant in the PtCoZSM5. The diffuse reflectance spectroscopy showed that Co2+ species in the monometallic solids were preferentially located at the main channels while in PtCoZSM5 these cations moved to higher coordination lattice sites. Through the combination of these tools, a much better understanding of the synergetic effect of Pt incorporated to CoZSM5 has been achieved. In view of these findings, related work previously published is revisited. [Copyright &y& Elsevier]

Tungsten catalysts supported on activated carbon were prepared using tungsten hexacarbonyl, ammonium tungstate, and tungsten pentaethoxide. The catalysts were pretreated in He, dry air, or wet air at 623 K for 6 h before being characterized by N2 adsorption at 77 K, temperature-programmed desorption, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy, and by testing their behavior in the decomposition reaction of isopropanol. The dispersion of the supported tungsten oxide phase and their surface acidity depended on the metal precursor and atmosphere of pretreatments. Thus, the highest dispersion and surface acidity were found for the catalyst prepared from W(CO)6 and the lowest dispersion for that prepared from (NH4)2WO4. Dry air gave the highest dispersion, whereas wet air yielded the highest surface acidity. Air pretreatments of the catalyst prepared from W(CO)6 seem to create metal oxide–support interactions, because of the very low particle size of the supported tungsten oxide phase and its homogeneous distribution. [Copyright &y& Elsevier]

The simultaneous formation of colloidal dispersions of Pd and Au metal particles protected by the organic polymer polyvinylpyrrolidone (PVP) in reducing alcohol solution was used for the synthesis of new silica-supported monometallic and bimetallic AuxPdy catalysts with different x/y ratios. The samples, with a 2 wt% total metal loading, after air calcinations at 673 K to remove the PVP, were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and FTIR spectra of chemisorbed CO. Formation of alloyed AuxPdy particles of different metal composition with consequent modification of their electronic and geometric properties was ascertained. The catalytic activity of the samples as a function of the gold–palladium content was tested in the hydrodesulfurization of thiophene and dibenzothiophene. For the former reaction, performed at low hydrogen pressure, the promoting effect of gold on the palladium activity was confirmed. For the latter reaction, carried out under high hydrogen pressure, pure gold catalyst exhibited larger activity and different selectivity compared to those of pure palladium catalyst. In both reactions the maximum activity was observed in correspondence of the bimetallic sample with 50/50 metal composition. The results are discussed with regard to electronic and ensemble size effects. [Copyright &y& Elsevier]