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Methane is an abundant and relatively clean fossil fuel resource; therefore, its utilization as a chemical feedstock has a major impact on the chemical industry. However, its inert nature makes direct conversion into value-added products difficult under mild conditions. Compared to the gas-phase selective oxidation of methane, there have been several recent advances in the liquid-phase conversion of methane. This review categorizes the reports on the liquid-phase selective oxidation of methane according to the solvent and oxidant used. The advantages and disadvantages of each approach are discussed. High yields of methyl bisulfate as a methanol precursor can be achieved using SO3 in sulfuric acid; however, more attention should be paid to the separation process and overall economic analysis. However, the aqueous-phase selective oxidation of methane with in situ generated H2O2 is quite promising from an environmental point of view, provided that an economical reducing agent can be used. Based on the current state-of-the-art on this topic, directions for future research are proposed. [ABSTRACT FROM AUTHOR]

The dry reforming of methane (DRM) is a promising method for controlling greenhouse gas emissions by converting CO2 and CH4 into syngas, a mixture of CO and H2. Ni-based catalysts have been intensively investigated for their use in the DRM. However, they are limited by the formation of carbonaceous materials on their surfaces. In this review, we explore carbon-induced catalyst deactivation mechanisms and summarize the recent research progress in controlling and mitigating carbon deposition by developing coke-resistant Ni-based catalysts. This review emphasizes the significance of support, alloy, and catalyst structural strategies, and the importance of comprehending the interactions between catalyst components to achieve improved catalytic performance and stability. [ABSTRACT FROM AUTHOR]

Ammonia decomposition is a key step in hydrogen production and is considered a promising practical intercontinental hydrogen carrier. In this study, 1 wt.% Ru/SiO2 catalysts were prepared via wet impregnation and subjected to calcination in air at different temperatures to control the particle size of Ru. Furthermore, silica supports with different surface areas were prepared after calcination at different temperatures and utilized to support a change in the Ru particle size distribution of Ru/SiO2. N2 physisorption and transmission electron microscopy were used to probe the textural properties and Ru particle size distribution of the catalysts, respectively. These results show that the Ru/SiO2 catalyst with a high-surface area achieved the highest ammonia conversion among catalysts at 400 °C. Notably, this is closely related to the Ru particle sizes ranging between 5 and 6 nm, which supports the notion that ammonia decomposition is a structure-sensitive reaction. [ABSTRACT FROM AUTHOR]

Methane is an abundant resource and its direct conversion into value-added chemicals has been an attractive subject for its efficient utilization. This method can be more efficient than the present energy-intensive indirect conversion of methane via syngas, a mixture of CO and H2. Among the various approaches for direct methane conversion, the selective oxidation of methane into methane oxygenates (e.g., methanol and formaldehyde) is particularly promising because it can proceed at low temperatures. Nevertheless, due to low product yields this method is challenging. Compared with the liquid-phase partial oxidation of methane, which frequently demands for strong oxidizing agents in protic solvents, gas-phase selective methane oxidation has some merits, such as the possibility of using oxygen as an oxidant and the ease of scale-up owing to the use of heterogeneous catalysts. Herein, we summarize recent advances in the gas-phase partial oxidation of methane into methane oxygenates, focusing mainly on its conversion into formaldehyde and methanol. [ABSTRACT FROM AUTHOR]

The effect of halide ion on the catalytic activity for the aqueous-phase partial oxidation of methane with H 2 O 2 generated in situ over Pd/C was examined. Various halide ions, including F-, Cl-, Br-, and I- were compared. Among them, Br- and I- are effective for the synthesis of H 2 O 2 from H 2 and O 2 , resulting in the synthesis of methane oxygenates from methane over Fe/ZSM-5. They show different product yields as a function of their concentrations. The highest total product yields were obtained with [KBr] = 5 mM and [KI] = 0.05 mM, respectively. Compared with Br-, the highest product yield was obtained with a much lower concentration of I-, guaranteeing that no detectable leaching of metal from Fe/ZSM-5 and Pd/C was found. The total productivity was 4.64 mmol/g cat. /h over Fe/ZSM-5 at 50 ℃ with H 2 O 2 generated in situ over Pd/C from H 2 and O 2 in the presence of 0.05 mM of KI. [Display omitted] • Partial oxidation of CH 4 was examined over Fe/ZSM-5 with in situ generated H 2 O 2. • The effect of halide anion was investigated over Pd/C. • Br- and I- are effective for the synthesis of methane oxygenates from methane. • The high productivity can be achieved in the presence of KI without metal leaching. [ABSTRACT FROM AUTHOR]

Direct conversion of methane into value‐added chemicals is a challenging but worthwhile subject. In this communication, the direct conversion of methane into methane oxygenates was achieved in an aqueous solution at room temperature using iron salts and Pd/C as catalysts and hydrogen peroxide as an oxidant. The hydrogen peroxide can be directly added or generated in situ from hydrogen and oxygen. The Pd/C catalyst greatly enhanced the reaction rate together with the iron salts. The effect of some parameters such as reaction temperature, reaction time, pH, acid type, and catalyst amount on the yields of the methane oxygenates was also investigated. When hydrogen peroxide was directly added, the turnover frequency (TOF), defined as the moles of methane oxygenates per moles of Fe per unit time, at 293 K was 29 h−1 at pH=2.3. The TOF at 293 K was 42 h−1 at pH=1.3 with in situ generated hydrogen peroxide from hydrogen and oxygen. [ABSTRACT FROM AUTHOR]

The direct oxidation of methane to methanol is considered challenging due to the intrinsically low reactivity of the C–H bond of methane and the formation of a large number of unstable intermediates (methanol, formaldehyde, and formic acid) relative to the yield of methane. However, promising advances have recently been reported in this area based on the use of electrochemical systems that differ from traditional thermal catalysis. In this review, the recent advances in direct and indirect electrochemical methane conversion with homogeneous catalysts are reviewed and discussed, especially under low-temperature conditions. Finally, the limitations of the current electrochemical methane conversion technology and future research directions are discussed. [ABSTRACT FROM AUTHOR]

RF plasma excitation of methane has been studied in an effort to optimize the reaction conditions for a selective partial oxidation of methane. The reaction products of RF-excited methane are C2 hydrocarbons such as ethane and acetylene when O2 is not used. The introduction of a few percent of O2, however, is found to switch the selectivity in favor of CO while CO2 formation is suppressed down to a level below a few percent. Interestingly, in the low O2 ratio regime (0-0.6), the selectivity between CO and C2 hydrocarbons is observed to vary systematically in response to the detailed reaction conditions, including flow rate, pressure and applied RF power, which are explained by the competition between coupling and partial oxidation reactions. Variation in the density and the residence time of the active species in the plasma is suggested to determine the overall reaction pathways. The present results suggest a possibility of a selective production of the partial oxidation products of methane such as CO with a high selectivity and a high conversion efficiency using controlled RF plasma from methane and O2. [ABSTRACT FROM AUTHOR]

The effect of the crystalline phase of alumina on ammonia decomposition over alumina-supported ruthenium (Ru) catalysts was examined. Various Ru catalysts supported on different alumina (α-Al 2 O 3 , κ-Al 2 O 3 , θ-Al 2 O 3 , δ-Al 2 O 3 , η-Al 2 O 3 , and γ-Al 2 O 3) were prepared using a wet impregnation method. The prepared catalysts were characterized using inductively coupled plasma-optical emission spectroscopy, N 2 physisorption, X-ray diffraction, transmission electron microscopy, and CO chemisorption. The Ru dispersion for Ru/Al 2 O 3 was reduced without a calcination step in the following order: Ru/α-Al 2 O 3 < Ru/κ-Al 2 O 3 < Ru/θ-Al 2 O 3 < Ru/δ-Al 2 O 3 < Ru/η-Al 2 O 3 < Ru/γ-Al 2 O 3. Among them, Ru/α-Al 2 O 3 showed the highest catalytic activity for ammonia decomposition. Moreover, the effect of calcination temperature before the reduction step was investigated. Ru particle size and morphology were confirmed to change through the calcination process. Ru/κ-Al 2 O 3 with Ru particle sizes ranging between 7 and 8 nm exhibited the highest ammonia decomposition rate among Ru/Al 2 O 3 catalysts calcined at different temperatures and reduced at 573 K. Therefore, Ru dispersion and its morphology, which can be controlled by the support and calcination temperature, are critical factors for hydrogen production through ammonia decomposition over Ru/Al 2 O 3 catalysts. [Display omitted] • NH 3 decomposition was performed over Ru/Al 2 O 3 catalysts. • The effect of the crystalline phases of alumina was evaluated. • The effect of the Ru dispersion and morphology was investigated. • All data support that NH 3 decomposition is a structure sensitive reaction. • The relationship between the catalytic activity and Ru dispersion is discussed. [ABSTRACT FROM AUTHOR]

The selective oxidation of methane into methane oxygenates such as CH3OH and HCOOH with O2 is a promising technology for direct methane conversion. This study successfully demonstrates the partial oxidation of methane over Pd−Fe/ZSM‐5 catalysts in water, where H2O2 was generated in situ from H2 and O2. A low Pd content is essential for preventing agglomeration of Pd nanoparticles, and intimate contact between Pd and Fe species is beneficial for achieving high yields of methane oxygenates. This one‐body catalyst showed better catalytic performance than that of previously reported ones, especially at low temperatures. 0.28 %Pd–0.56 %Fe/ZSM‐5 exhibited a stable catalytic performance in a continuous flow reactor. [ABSTRACT FROM AUTHOR]

Highlights: [•] The dehydration of d-xylose was examined over dealuminated and desilicated H-ZSM-5. [•] The total amount of acid sites decreased significantly for desilicated H-ZSM-5. [•] The fraction of Brønsted acid sites increased after dealumination of H-ZSM-5. [•] The fraction of Brønsted acid sites decreased after desilication of H-ZSM-5. [•] The furfural selectivity increased with increasing dealumination in H-ZSM-5. [ABSTRACT FROM AUTHOR]

Abstract: We prepared Ru catalysts supported on various aluminum oxides with different crystalline phases, viz. α-Al2O3, κ-Al2O3, γ-Al2O3, η-Al2O3, δ-Al2O3 and θ-Al2O3, by the incipient wetness method and applied them to the selective CO oxidation in a hydrogen-rich stream. For comparison, the complete CO oxidation in the absence of H2 was also carried out over the same catalysts. Ru/α-Al2O3 showed the highest CO conversion among the tested catalysts, especially at low temperatures, irrespective of the presence of H2. For all of the catalysts, the catalytic activity for CO oxidation was much suppressed in the absence of H2 compared with that in the presence of H2. Several techniques: N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), CO chemisorption, temperature-programmed oxidation (TPO), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of CO2 with mass spectroscopy and transmission electron microscopy (TEM) were employed to characterize the catalysts. The least amount of chemisorbed CO and CO2 was obtained at room temperature over Ru/α-Al2O3. The least amount of O2 was chemisorbed during TPO and the oxidized Ru species could be fully reduced in the presence of hydrogen at the lowest temperature over Ru/α-Al2O3 among the Ru/Al2O3 catalysts. Ru/α-Al2O3 can reduce a high inlet concentration of CO to less than 10ppm even in the presence of H2O and CO2 over a wide temperature range. [Copyright &y& Elsevier]

Abstract: We prepared various Ru catalysts supported on different supports such as yttria-stabilized zirconia (YSZ), ZrO2, TiO2, SiO2 and γ-Al2O3 with a wet impregnation method. We applied them to the selective CO removal in a hydrogen-rich stream via the preferential CO oxidation (PROX) and the selective CO methanation simultaneously. Among them, Ru/YSZ showed the highest CO conversion especially at low temperatures. Several measurements: the N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), the CO chemisorptions, the temperature-programmed oxidation (TPO), the temperature-programmed reduction (TPR), the temperature-programmed desorption (TPD) of CO2 with mass spectroscopy and the transmission electron microscopy (TEM), were conducted to characterize the catalysts. No linear correlation can be found between the amount of CO chemisorbed at 300K and the PROX activity. On the other hand, the facile activation of O2 appeared to be closely related to the high PROX activity, judging by the TPO experiment. In addition, the strong adsorption of CO2 suppressed the low-temperature PROX activity. Ru/YSZ can be easily oxidized and also reduced at low temperatures. It is found that Ru/YSZ uptakes only small amounts of CO2, which can be desorbed at low temperatures. Ru/YSZ can reduce the high inlet CO concentration to be less than 10ppm even in the presence of H2O and CO2. [Copyright &y& Elsevier]

Abstract: We conducted a comparative study for the preferential CO oxidation (PROX) over supported noble metal catalysts. The CO chemisorption in the absence and presence of H2, the O2 chemisorption, the temperature-programmed oxidation (TPO), the temperature-programmed reduction (TPR) after O2 chemisorption and the transmission electron microscopy (TEM) were conducted to characterize the catalysts. Commercial catalysts such as 1wt.% Pt/γ-Al2O3, 0.5wt.% Ru/γ-Al2O3, 0.5wt.% Rh/γ-Al2O3, 5wt.% Pt/γ-Al2O3, 5wt.% Ru/γ-Al2O3, and 5wt.% Rh/γ-Al2O3 were utilized. Among them, 5wt.% Ru/γ-Al2O3 showed the highest PROX activity. This catalyst can be considered to be promising because it can reduce the high inlet CO concentration to be less than 10ppm at low temperatures where the reverse water–gas shift reaction can be minimized. No detectable amount of chemisorbed O2 was measured at 373K over 1wt.% Pt/γ-Al2O3, 0.5wt.% Rh/γ-Al2O3 and 5wt.% Pt/γ-Al2O3. The moderate degree of CO and O2 chemisorption at reaction temperatures appeared to be essential for the optimum PROX activity. Although 0.5wt.% Ru/γ-Al2O3 and 5wt.% Ru/γ-Al2O3 have the similar particle size distribution based on TEM analysis, the latter catalyst with smaller amount of chemisorbed CO and O2 per Ru metal showed much better PROX activity. Based on TPO and TPR result, 0.5wt.% Ru/γ-Al2O3 can be oxidized at lower temperatures but can be reduced at higher temperatures compared with 5wt.% Ru/γ-Al2O3. Therefore, the easily reducible Ru species can give us the better PROX activity over a wide reaction temperature for Ru catalysts. [Copyright &y& Elsevier]

Abstract: We conducted a comparative study for the water-gas shift (WGS) reaction over ceria-promoted Pt catalysts supported on various supports such as γ-Al2O3, SiO2, TiO2 (P-25), CeO2, SiO2-Al2O3, yttria-stabilized zirconia (YSZ) and ZrO2 in a rather severe reaction condition such as 6.7vol.% CO, 6.7vol.% CO2, and 33.2vol.% H2O in H2. Among them, Pt-Ce/TiO2 showed the highest WGS activity especially at low temperatures. The effect of preparation sequences on the catalytic activity was also examined for ceria-promoted Pt supported on TiO2 and Pt-Ce/TiO2 prepared with a single-step co-impregnation method showed the highest water-gas shift activity. The CO chemisorptions, the temperature-programmed reduction (TPR), an inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and a transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX) were conducted to characterize catalysts. The close correlation between the low-temperature water-gas shift activity and the amounts of chemisorbed CO as well as the degree of interaction between Pt and ceria has been observed. This Pt-Ce/TiO2 showed the more stable catalytic activity in the cyclic operation and the start-up/shut-down operation compared with the conventional Pt-Ce/CeO2. [Copyright &y& Elsevier]

Abstract: The catalytic stability of MoO3/SiO2 and TiO2/SiO2, which have been reported to be active for transesterification between dimethyl carbonate and phenol, was examined in a batch reactor for the same reaction. X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and the temperature programmed oxidation (TPO) were conducted to characterize the catalysts. The gradual decrease in the activity was observed over both catalysts with increasing the number of a batch reaction. The strong adsorption of reactants was observed from the temperature programmed oxidation experiment. The deactivated MoO3/SiO2 can be regenerated after oxidation in air at 823K. However, the deactivated TiO2/SiO2 can be only partially regenerated even after oxidation in air at 973K. Some of the Mo species in MoO3/SiO2 were leached out during a reaction. This dissolved homogeneous Mo species appeared to take part in this reaction. [Copyright &y& Elsevier]

Abstract: In this review, recent works related to the selective CO removal in a H2-rich stream for the application of the low-temperature fuel cell are discussed. The membrane separation, the selective CO hydrogenation, and the preferential CO oxidation (PROX) have been generally studied to meet the requirement for the polymer electrolyte membrane fuel cell (PEMFC) where the CO concentration should be controlled to be less than 10ppm not to degrade the electrochemical performance of Pt anode. For the membrane separation, the thin layer of Pd-based alloy metal on the porous ceramic material coupled with the catalytic purification is the most advanced method at present. For PROX catalysts, supported Ru catalysts and Pt-based alloy catalysts have been successfully developed so far. The combination of highly selective PROX catalysts and the CO methanation catalyst can provide the extended temperature range to achieve the acceptable CO removal. Because each method has presently its own weak points, the further advance is still in need. The non-noble metal-based membrane requiring smaller pressure differentials is highly plausible in the membrane separation. The highly selective catalyst for CO methanation in the presence of excess CO2 and H2O can simplify the CO removal step. The PROX catalyst should be operative over a wide reaction temperature as well as at low temperatures not to cause the reverse water–gas shift reaction. During the development of these catalysts, the progress on the high-temperature PEM fuel cell or the CO-tolerant anode should be carefully evaluated. [Copyright &y& Elsevier]

Fe-ZSM-5 is an active catalyst for the selective oxidation of methane with H 2 O 2 in liquid water. To prepare the active Fe-ZSM-5 catalyst, the effect of the Fe precursor on the catalytic performance was examined. Additionally, two preparation methods, wet impregnation (WI) and ion-exchange (IE), were also applied. The prepared catalysts were characterized using various techniques, such as nitrogen physisorption, X-ray diffraction, UV–Vis spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy after NO adsorption (NO-FTIR). Fe-ZSM-5 prepared from FeCl 2 appears to be the most active among the Fe-ZSM-5 catalysts prepared from FeCl 2 , FeSO 4 , Fe(CH 3 CO 2) 2 , FeCl 3 , Fe 2 (SO 4) 3 , Fe(C 5 H 7 O 2) 3 , and Fe(NO 3) 3 using the WI method. For Fe-ZSM-5 catalysts prepared using the IE method, divalent Fe precursors, such as FeSO 4 , FeCl 2 , and Fe(CH 3 CO 2) 2 , are better than trivalent Fe precursors, such as Fe 2 (SO 4) 3 , FeCl 3 , and Fe(NO 3) 3 , in terms of catalytic activity. The active catalyst has the dominant extra-framework Fe2+ species probed with UV–Vis spectroscopy and NO-FTIR. [Display omitted] • Partial oxidation of CH 4 with H 2 O 2 in water was examined over Fe-ZSM-5. • The effect of Fe precursor during the catalyst preparation was investigated. • The active sites were probed with FT-IR spectroscopy after NO adsorption. • Correlation was made between the activity and the peak intensity in NO-FTIR spectra. [ABSTRACT FROM AUTHOR]

Abstract: Manganese oxide catalysts prepared by a precipitation method with various precipitants were investigated for the low temperature selective catalytic reduction (SCR) of NOx with NH3 in the presence of excess O2. Various characterization methods such as N2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and X-ray absorption near edge structure (XANES) were conducted to probe the physical and chemical properties of MnOx catalysts. The active MnOx catalysts, precipitated with sodium carbonate and calcined in air at moderate temperatures such as 523K and 623K, have the high surface area, the abundant Mn4+ species, and the high concentration of surface oxygen on the surface. The amorphous Mn3O4 and Mn2O3 were mainly present in this active catalyst. The carbonate species appeared to help adsorb NH3 on the catalyst surface, which resulted in the high catalytic activity at low temperatures. [Copyright &y& Elsevier]

Abstract: Selective CO oxidation in the presence of excess hydrogen was studied over metal oxides (CoO and CuO–CeO2), supported gold catalysts (Au/γ-Al2O3, Au/CuO, Au/CeO2/γ-Al2O3, Au/CuO–CeO2 and Au/CeO2), and supported Pt catalysts (Pt/γ-Al2O3, Pt–Ni/γ-Al2O3, and Pt–Co/γ-Al2O3). The methanation was dominant over CoO in the presence of excess H2. CuO–CeO2 was quite selective for CO oxidation at low temperatures. However, the presence of CO2 and H2O retarded its catalytic activity. No beneficial effect to CO2 selectivity was observed when Pt, Ru, Ni, and Co was added to CuO–CeO2 as a modifier. Supported gold catalysts showed the high CO conversion at low temperatures. However, the CO2 selectivity decreased noticeably with increasing H2 concentration in a reactant. Pt–Ni/γ-Al2O3 showed the highest CO conversion with a high CO2 selectivity over a wide reaction temperature among above catalysts examined at the same reaction condition. This catalyst also showed the best performance in the presence of 2vol.% H2O and 20vol.% CO2. [Copyright &y& Elsevier]

Abstract: Cu–Mn mixed oxides were prepared by a co-precipitation method and applied for low temperature NO reduction with NH3 in the presence of excess oxygen. Effects of [Cu]/[Mn] ratio and calcination temperatures on NOx conversions were investigated. Cu–Mn oxide catalysts containing small amounts of copper showed the complete NOx conversion in a wide range of reaction temperature from 323 to 473K. This catalyst showed a reversible deactivation due to the presence of water vapor and SO2. Different catalytic activities of Cu–Mn mixed oxides could be attributed mainly to surface areas and the crystalline nature. [Copyright &y& Elsevier]

Active states of palladium and copper for the oxidative carbonylation of phenol and bisphenol-A were investigated using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) for Pd and Cu K-edges. The initial states of Pd and Cu were carbon-supported metallic Pd and cuprous oxide, respectively. During oxidative carbonylation, however, the metallic character of palladium was enhanced, as indicated by Pd K-edge XANES spectra taken before and after the reaction. Furthermore, Pd&z.sbnd;Pd coordination number increased from ca. 6.0 to 11.0, as determined by the quantitative EXAFS analyses of Pd K-edge. The initial crystalline cuprous oxide was converted by reaction with Bu4NBr into an unusual linear cuprous dibromide complex stabilized by tetrabutylammonium cation. Qualitative XANES and EXAFS analyses of Cu K-edge identified the structural and electronic configuration of the cuprous complex that was found to be the active main catalyst. There was a direct correlation between the formation of the cuprous complex and the catalytic activity and selectivity. Based on these results, a possible catalytic reaction scheme was proposed for the oxidative carbonylation of phenols with the catalytic system of Pd/C, an inorganic cuprous compound and Bu4NBr. [Copyright &y& Elsevier]

Copper- and vanadium-catalyzed oxidation of methane into methyl trifluoroacetate and formic acid with in situ generated H2O2 from H2 and O2 over Pd/C was investigated in trifluoroacetic acid (TFA) and/or trifluoroacetic anhydride (TFAA) as a solvent. Metallic palladium was responsible for the in situ generation of hydrogen peroxide from dihydrogen and dioxygen. Divalent copper hydroperoxide and monoperoxomonovanadate, VO(O2)+, seemed to be related to C&z.sbnd;H bond activation. The radical chain reaction did not occur in either copper- or vanadium-catalyzed methane oxidation. However, methyl radical appeared to be produced in vanadium system but not in copper system. [Copyright &y& Elsevier]

Effects of various metal complexes of Ce, Co, Mn, and Cu compounds and of initial states of Pd with different particle sizes were investigated on coupled oxidative carbonylations of bisphenol-A (BPA) and phenol over activated carbon-supported metallic palladium (Pd/C). In the presence of Ce(CH3COO)3 as the cocatalyst, homogeneous Pd(CH3COO)2 showed a better activity than Pd/C as the main catalyst. From screening of the various inorganic cocatalysts, Cu2O was chosen as the best partner with the activated carbon-supported metallic palladium. More interestingly, this heterogeneous Pd/C-Cu2O catalyst system was superior to the homogeneous catalyst systems such as Pd(CH3COO)2-Ce(CH3COO)3 or Pd(CH3COO)2-Cu2O because it provided increased conversions of bisphenol-A and selectivities to desired para-position carbonylated products. The active phase of palladium in this catalyst system appeared to be metallic Pd, as evidenced by a stronger metallic character of palladium observed after the reaction with X-ray absorption of near edge structure (XANES) of Pd K-edge. In the presence of Pd/C, the nature of metal and ligand of the inorganic cocatalyst significantly affected the catalytic activity and selectivity. However, the initial state of supported Pd showed a negligible effect, even though the metallic character of Pd varied drastically due to increasing Pd loadings or reduction temperatures. [Copyright &y& Elsevier]

In this study, a Cu-promoted Fe/ZSM-5 catalyst was examined to reveal the effects of Cu species in selective oxidation of methane into methane oxygenates using H2O2 in water. Cu/ZSM-5, Cu-Fe/ZSM-5, and Fe/ZSM-5 catalysts were prepared using wet impregnation, solid-state ion exchange, and ion-exchange methods. Various techniques, including nitrogen physisorption, temperature-programmed reduction with H2, UV-vis spectroscopy, and FT-IR spectroscopy after NO adsorption, were utilized to characterize the catalysts. The promotional effect of Cu on the Cu-Fe/ZSM-5 catalyst in terms of methanol selectivity was confirmed. The preparation method has a considerable influence on the catalyst performance, and the ion-exchange method is the most effective. However, leaching of the Cu species was observed during this reaction, which can affect the quantification of formic acid by 1H-NMR. The homogeneous Cu species increase hydrogen peroxide decomposition and CO2 selectivity, which is undesirable for this reaction. [ABSTRACT FROM AUTHOR]

Liquid-phase selective oxidation of methane into methane oxygenates, including methanol and formic acid, with molecular oxygen was investigated using Fe-zeolites and Pd/activated carbon in the presence of molecular hydrogen as a reducing agent. Various Fe-zeolites such as Fe-ZSM-5, Fe-mordenite, Fe-β, Fe-Y, and Fe-ferrierite were prepared by ion-exchange and compared for this reaction. Among them, Fe-ZSM-5 was selected for further study because this catalyst showed high activity in the selective oxidation of methane with relatively less leaching. Further, the effect of reaction temperature, pH, and the amount of catalyst was examined, and detailed investigations revealed that the leached Fe species, which were facilitated in the presence of acid, were mainly responsible for methane oxidation under the given reaction conditions. [ABSTRACT FROM AUTHOR]

Front Cover: Aqueous-Phase Selective Oxidation of Methane with Oxygen over Iron Salts and Pd/C in the Presence of Hydrogen (ChemCatChem 17/2019) Shows the catalyst system composed of homogeneous iron salt and heterogeneous Pd/C which are responsible for aqueous-phase methane oxidation with oxygen in the presence of hydrogen even at low temperatures near 0 °C. When hydrogen peroxide was directly added, the turnover frequency (TOF), defined as the moles of methane oxygenates per moles of Fe per unit time, at 293 K was 29 h SP -1 sp at pH = 2.3. [Extracted from the article]

The front cover artwork for Issue 17/2019 is provided by Jongkyu Kang and Prof. Eun Duck Park at Ajou University (Republic of Korea). The image shows the catalyst system composed of homogeneous iron salt and heterogeneous Pd/C which are responsible for aqueous‐phase methane oxidation with oxygen in the presence of hydrogen even at low temperatures near 0 °C. See the Communication itself at https://doi.org/10.1002/cctc.201900919. [ABSTRACT FROM AUTHOR]

Surface hydrophobicity is an important factor in controlling the catalytic activity of heterogeneous catalysts in various reactions, particularly liquid-phase reactions using water as the (co)solvent. In this study, the surface hydrophobicity of Fe-ZSM-5 was successfully controlled using a simple coating method in which furfuryl alcohol was used as the carbon precursor. Various techniques, such as N2 physisorption, temperature-programmed desorption of ammonia, and contact angle measurements of water droplets, were used to characterize the catalysts. Fe-ZSM-5 catalysts with different degrees of hydrophobicity were used for the aqueous-phase selective oxidation of methane with H2O2. The positive effect of the surface carbon coating on the catalytic performance was confirmed when the carbon content was not sufficiently high to block the pores. [ABSTRACT FROM AUTHOR]

We investigated the influence of the reduction method on the preferential oxidation of CO in H2 (CO-PROX) over Au/La2O3/Al2O3 catalysts. An Au/La2O3/Al2O3 sample, prepared using deposition–precipitation with urea, was reduced by chemical reduction with NaBH4 or glycerol. Several techniques, such as diffuse-reflectance infrared Fourier-transform spectroscopy after CO adsorption (CO-DRIFTS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were used to characterize the catalysts. Additionally, the catalysts were examined by in situ DRIFTS during methanol decomposition. The results reveal that the reduction method affects the average particle size and electronic state of gold, as well as the characteristics of the CO–Au0 interactions. The best CO-PROX performance was observed for the catalyst chemically reduced using NaBH4 with a NaBH4/Au molar ratio of 35. This catalyst contained gold particles with size of ~4 nm, for which the XPS binding energy was lower than that of metallic gold. [ABSTRACT FROM AUTHOR]

The direct conversion of methane into methanol is an ideal, highly promising process; however, its application remains challenging. Herein, a systematic study was carried out on the continuous gas-phase oxidation of methane into methanol with steam in the absence and presence of O 2 over Cu-mordenites (Cu-MOR) with various Cu loadings. The methanol productivity depended on the Cu/Al ratio of the Cu-MOR; it could be maximized by selecting the optimum Cu/Al ratio. Methanol productivity increased as the concentration of O 2 in the feed increased from 0 to 100 ppm. However, methanol selectivity decreased when the O 2 concentration in the feed was above 25 ppm. The stable methanol production rates based on the Cu content were 0.14 and 0.70 mol CH 3 OH/mol Cu/h at 400 °C over a Cu-MOR catalyst with 6.2 wt% Cu under anaerobic conditions and one with 3.0 wt% Cu in the presence of 25 ppm O 2 , respectively. [Display omitted] • Continuous gas-phase oxidation of methane into methanol was examined over Cu-mordenites (Cu-MOR). • The methanol productivity depends on the Cu/Al ratio of the Cu-MOR. • The methanol productivity increases with increasing O 2 concentration in the feed from 0 to 100 ppm. • The methanol selectivity decreases with increasing O 2 concentration above 25 ppm. [ABSTRACT FROM AUTHOR]

• Ni/SiO 2 catalysts were prepared from aqueous Ni(NO 3) 2 solutions by the precipitation method using Na 2 SiO 3. • This is a simple but efficient method to prepare well-dispersed NiO on silica. • The prepared catalysts were active for two model reactions, benzene hydrogenation and CO methanation. Ni/SiO 2 catalysts with high Ni content were prepared from aqueous Ni(NO 3) 2 solutions by the precipitation method using Na 2 SiO 3 as a silica precursor and precipitant. This is a simple but efficient method to prepare well-dispersed NiO on silica, which can be further transformed to Ni/SiO 2 through an additional reduction process. Various techniques such as nitrogen physisorption, X-ray diffraction (XRD), temperature-programmed reduction with hydrogen (H 2 -TPR), hydrogen chemisorption, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) were employed to characterize the catalysts. The prepared catalysts were applied to two model reactions, benzene hydrogenation and CO methanation. The catalyst showed significantly enhanced performance for these reactions compared to core-shell Ni@SiO 2 catalysts and conventional Ni/SiO 2 catalysts prepared by wet impregnation. [ABSTRACT FROM AUTHOR]

Ni/SiC and Ni/SiO2 catalysts prepared by both wet impregnation (WI) and deposition-precipitation (DP) methods were compared for CO and CO2 methanation. The prepared catalysts were characterized using N2 physisorption, temperature-programmed reduction with H2 (H2-TPR), H2 chemisorption, pulsed CO2 chemisorption, temperature-programmed desorption of CO2 (CO2-TPD), transmission electron microscopy, and X-ray diffraction. H2-TPR analysis revealed that the catalysts prepared by DP exhibit stronger interaction between the nickel oxides and support than those prepared by WI. The former catalysts exhibit higher Ni dispersions than the latter. The catalytic activities for both reactions over Ni/SiC and Ni/SiO2 catalysts prepared by WI increase on increasing the Ni content from 10 to 20 wt%. The Ni/SiC catalyst prepared by DP shows higher catalytic activity for CO and CO2 methanation than that of the Ni/SiC catalyst prepared by WI. Furthermore, it exhibits the highest catalytic activity for CO methanation among the tested catalysts. The high Ni dispersion achieved by the DP method and the high thermal conductivity enabled by SiC are beneficial for both CO and CO2 methanation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rh–C i /HCO 3 − hetero-/homogenous dual co-catalysts were introduced on the BiVO 4 surface. • Rh–C i /HCO 3 − dual co-catalyst system improved the water oxidation activity of BiVO 4. • This system enhances the charge injection efficiency and stabilizes the photoelectrochemical water oxidation kinetics. • BiVO 4 decorated with Rh–C i /HCO 3 − exhibited a higher photocurrent than bare BiVO 4. Bismuth vanadate is one of the most efficient photoanode materials for solar water-splitting. However, its performance is limited by two main factors: poor charge separation and slow water oxidation kinetics. Herein, Rh–C i /HCO 3 − hetero-/homogenous dual co-catalysts were introduced on the BiVO 4 surface to improve the water oxidation performance. This Rh–C i /HCO 3 − dual co-catalyst system improved the water oxidation activity of BiVO 4 by enhancing the charge injection efficiency and stabilizing the photoelectrochemical water oxidation kinetics. BiVO 4 decorated with Rh–C i /HCO 3 − exhibited a higher photocurrent (2.011 mA∙cm−2) at 1.23 V RHE than bare BiVO 4 (1.217 mA∙cm−2). [ABSTRACT FROM AUTHOR]

[Display omitted] • The CuInS 2 photocathode surface was modified with MoS x and noble metal co-catalyst, Pt, or Ru. • Ru-decorated photocathode shows unexpected higher HER activity than Pt-decorated photocathode. • Physicochemical and photoelectrochemical characterizations were carried out to reveal PEC activity differences. • The semiconductor/metal interface with a high ϕ m of Ru enhanced the PEC activity of the photocathode. In this work, the photoelectrochemical H 2 production activity of CuInS 2 photocathodes is investigated after sequential surface modification with a-MoS x , Pt, or Ru. Although Ru has much inferior electrocatalytic activity to Pt for hydrogen evolution reaction (HER), a Ru-modified CuInS 2 /a-MoS x photocathode shows higher photoelectrochemical (PEC) activities than a Pt-modified one. X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and other (photo)electrochemical characterizations were carried out for the surface-modified CuInS 2 photocathode to reveal the origin of the high PEC activity. The energy level of Ru on CuInS 2 /a-MoS x photocathodes is more suitable for the electron transfer between semiconductor–metal-electrolytes, and it leads to a fast electron transient time during PEC reaction by the improved carrier lifetime. This result implies that the Ru modification of photocathodes can be one of potential strategies for tuning band alignment and improving PEC activities. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) H2 production from water using solar energy is an ideal and environmentally friendly process. CuInS2 is a p-type semiconductor that offers many advantages for PEC H2 production. Therefore, this review summarizes studies on CuInS2-based PEC cells designed for H2 production. The theoretical background of PEC H2 evolution and properties of the CuInS2 semiconductor are initially explored. Subsequently, certain important strategies that have been executed to improve the activity and charge-separation characteristics of CuInS2 photoelectrodes are examined; these include CuInS2 synthesis methods, nanostructure development, heterojunction construction, and cocatalyst design. This review helps enhance the understanding of state-of-the-art CuInS2-based photocathodes to enable the development of superior equivalents for efficient PEC H2 production. [ABSTRACT FROM AUTHOR]

The electrochemical activation of CuInS2/MoSx for photoelectrochemical (PEC) H2 production was revealed for the first time through in operando Raman spectroscopy. During the activation process, the initial metallic MoSx phase was transformed to semiconducting MoSx, which facilitates charge carrier transfer between CuInS2 and MoSx. Ex situ X‐ray photoelectron spectroscopy and Raman spectroscopy suggest the existence of MoO3 after the activation process. However, apart from contradicting these results, in operando Raman spectroscopy revealed some of the intermediate steps of the activation process. [ABSTRACT FROM AUTHOR]

The electrochemical activation of CuInS2/MoSx for photoelectrochemical (PEC) H2 production was revealed for the first time through in operando Raman spectroscopy. During the activation process, the initial metallic MoSx phase was transformed to semiconducting MoSx, which facilitates charge carrier transfer between CuInS2 and MoSx. Ex situ X‐ray photoelectron spectroscopy and Raman spectroscopy suggest the existence of MoO3 after the activation process. However, apart from contradicting these results, in operando Raman spectroscopy revealed some of the intermediate steps of the activation process. [ABSTRACT FROM AUTHOR]

Green hydrogen is increasingly recognized as one of the most promising options to decarbonize the energy and transport sector to achieve the goal of climate neutrality, but its low volumetric density presents significant challenges that need to be addressed. Because of their ease of handling and transportability, liquid carriers such as liquid organic hydrogen carriers (LOHCs) and ammonia are particularly appealing. This work presents a comparative sustainability analysis of three liquid carriers: liquid hydrogen, liquid ammonia, and synthetic natural gas, and the three promising LOHCs (methanol, di-benzyl toluene, and methylcyclohexane), based on rigorous economic and environmental evaluations. The overall results indicate that by 2050, the promising carriers for small- to medium-level market penetrations (i.e., 50 000 kg d−1) would be ammonia and methanol, with levelized costs of 3.60 and 3.78 $ per kg H2, respectively, while that for high-level market penetrations (i.e., 57.1 Mt per year) is LH2 with a levelized cost of 2.12 $ per kg H2. LH2 is a promising carrier from an environmental perspective because it does not have an energy-intensive dehydrogenation stage. Finally, policy implications are presented as these necessitate the development of a strategic policy framework around the globe to comply with the legal requirements set forth by the United Nations, such as the Paris Agreement and Sustainable Development Goals. [ABSTRACT FROM AUTHOR]

The specific catalytic activity of a supported metal catalyst increases with an increase in the number of active sites per mass of catalyst, which can be accomplished by increasing the metal content and/or decreasing the particle size of the metal. However, this leads to sintering of metal particles during the reaction, especially in highly exothermic reactions such as CO methanation. In this study, we prepared different SiO 2 -supported Ni catalysts by wet impregnation and sol–gel methods, and applied them to CO methanation. The prepared catalysts were characterized with N 2 physisorption, X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), temperature-programmed reduction with H 2 (H 2 -TPR), and transmission electron microscopy (TEM). Some problems associated with the wet impregnation method, such as sintering of Ni and the inability to load the silica with large amounts of Ni, were avoided by using the sol–gel method, in which size-controlled NiO was first synthesized using a polymer stabilizing agent, and then coated with a mesoporous silica shell through a polymerization approach. The prepared 55 wt% Ni@SiO 2 catalyst exhibited the co-presence of Ni nanoparticles (mean size = 8.0 ± 4.4 nm) and nanorods (mean length = 15.5 ± 13 nm, mean width = 8.1 ± 4.4 nm). This catalyst was far superior for CO methanation than the conventional 33 wt% Ni/SiO 2 catalyst prepared by wet impregnation, in which the Ni particle size was 24.5 nm. The 55 wt% Ni@SiO 2 catalyst also exhibited excellent catalytic performance for selective CO methanation in the presence of an excessive amount of CO 2 . [ABSTRACT FROM AUTHOR]

CO2 methanation is a promising reaction for utilizing CO2 using hydrogen generated by renewable energy. In this study, CO and CO2 methanation were examined over ceria-supported cobalt catalysts with low cobalt contents. The catalysts were prepared using a wet impregnation and co-precipitation method and pretreated at different temperatures. These preparation variables affected the catalytic performance as well as the physicochemical properties. These properties were characterized using various techniques including N2 physisorption, X-ray diffraction, H2 chemisorption, temperature-programmed reduction with H2, and temperature-programmed desorption after CO2 chemisorption. Among the prepared catalysts, the ceria-supported cobalt catalyst that was prepared using a wet impregnation method calcined in air at 500 °C, and reduced in H2 at 500 °C, showed the best catalytic performance. It is closely related to the large catalytically active surface area, large surface area, and large number of basic sites. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study revealed the presence of carbonate, bicarbonate, formate, and CO on metallic cobalt. [ABSTRACT FROM AUTHOR]

Highlights: [•] The hydrogenolysis of cellulose was examined over Ni/W/SiO2 catalysts. [•] The crystallite size of W increased with average pore size of support. [•] The crystallite size of W increased with reduction temperature. [•] The yield of polyols increased on decreasing the crystallite size of W. [•] The amount of surface acid site decreased with increasing crystallite size of W. [ABSTRACT FROM AUTHOR]

Methane has been reported to be directly converted into value-added products through various methods. Among them, photoelectrochemical (PEC) methane conversion is considered an eco-friendly method because it utilizes solar light and is able to control the selectivity to different products by means of application of an external bias. Recently, some PEC methane conversion systems have been reported, but their performance efficiencies are relatively lower than those of other existing thermal, photocatalytic, and electrochemical systems. The detailed mechanism of methane activation is not clear at this stage. In this review, various catalytic materials and their roles in the reaction pathways are summarized and discussed. Furthermore, promising semiconductor materials, co-catalysts, and oxidants have also been proposed. Finally, direct and indirect pathways in the design of the PEC methane conversion system have been discussed. [ABSTRACT FROM AUTHOR]

The catalytic activity of metal oxide-supported Pt-MO x (M=Mo, W, Ce, V) catalysts was investigated for methanol reforming to hydrogen at low temperatures with varied reaction pressures in gaseous to aqueous phase regimes. The Pt-MoO x/TiO2 catalysts prepared through co-impregnation of the precursors demonstrated unprecedentedly high catalytic activities compared with the previously reported Pt-based catalysts, which showed an order of magnitude higher hydrogen production turnover rates with extremely low CO selectivities. The morphological and electrochemical characteristics of the dispersed Pt-MoO x nanoclusters were largely affected by the impregnation method and the Mo/Pt atomic ratio. The Pt-MoO x nanoclusters consisting of metallic state Pt and MoO x moieties of high site density and reducibility capable of Mo6+ to Mo5+ redox transition promoted the marked rate enhancements in methanol reforming to hydrogen at low temperatures. These highly active catalysts offer opportunities in the direct embedding of fuel processing in polymer electrolyte membrane fuel cells through the internal thermal integration of exothermic electrochemical reactions with endothermic fuel reforming for hydrogen production. [ABSTRACT FROM AUTHOR]

Abstract: The direct conversion of cellulose into polyols over Ni/W/SiO2-Al2O3 catalysts with different Al molar fractions was examined. For comparison, Cu/W/SiO2-Al2O3, Fe/W/SiO2-Al2O3, and Co/W/SiO2-Al2O3 were also evaluated. The bulk crystalline structure was determined using X-ray diffraction (XRD). The surface acidity was probed via temperature-programmed desorption of ammonia (NH3-TPD). The textural properties were investigated using N2 physisorption. The metal contents were confirmed via inductively coupled plasma–atomic emission spectroscopy (ICP-AES). Among the various metal catalysts, Ni/W/SiO2-Al2O3 was confirmed to be the most favorable for hydrogenolysis of cellulose into polyols. The effect of the Al molar fraction in SiO2-Al2O3 on this reaction over Ni/W/SiO2-Al2O3 was also investigated. It was found that the polyol yield was closely related to the total acidity of the support. Compared to Ni/W/SBA-15, Ni/W/SiO2-Al2O3 (Al/(Al+Si)=0.6) showed better stability during the recycling test. The catalyst deactivation was confirmed to be caused by metal leaching. [Copyright &y& Elsevier]

Abstract: We prepared various Ru catalysts supported on silicas with different surface areas by an incipient wetness impregnation method and applied them in selective CO oxidation in a H2-rich stream. For comparison, complete CO oxidation was also examined. The physical properties were probed with N2 physisorption. The Ru dispersion was measured with CO chemisorption and transmission electron microscopy (TEM). The interaction between the catalyst surface and a reactant was examined with O2 chemisorption, temperature-programmed oxidation (TPO), and temperature-programmed reduction (TPR). The BET surface area and total pore volume of the silica decreased with increasing calcination temperature. The average pore diameter of the silica increased with calcination temperature. The existence of micropores was not observed in the silica calcined in air at temperatures of 1103K and above. The amount of CO and O2 chemisorbed on Ru/SiO2 at 300K decreased with decreasing surface area of the silica. The particle size of Ru metal in Ru/SiO2 generally increased with decreasing surface area of the silica. Ru/SiO2 with a larger Ru particle size showed superior catalytic activities for the complete CO oxidation and the selective CO oxidation in a H2-rich stream, compared to Ru/SiO2 with a smaller Ru particle size, which might be due to the resistance to oxidation of Ru metal into RuO x species. The Ru particle size also affects the fraction of active surface oxygen. Selected Ru/SiO2 catalysts can reduce a high inlet CO concentration to less than 10ppm even in the presence of H2O and CO2. [Copyright &y& Elsevier]

Abstract: Dehydration of methanol into dimethyl ether was carried out over aluminum oxides prepared via a surfactant-templated method in the presence of different surfactants. The surfactant strongly affected the final physicochemical properties of the alumina as well as the catalytic activity: alumina prepared using CH3(CH2)14COOH and that synthesized in the presence of P123 exhibited the highest and least catalytic activity, respectively. The good correlation between the catalytic activity and surface hydrophilicity of alumina implied surface hydrophilicity and surface acidity affect the catalytic activity for the dehydration reaction. [Copyright &y& Elsevier]

Abstract: The water–gas shift (WGS) reaction was examined over Pt and Pt–CeO x catalysts supported on Ce x Zr1−x O2 (Ce0.05Zr0.95O2, Ce0.2Zr0.8O2, Ce0.4Zr0.6O2, Ce0.6Zr0.4O2, Ce0.7Zr0.3O2 and Ce0.8Zr0.2O2) under severe reaction conditions, viz. 6.7 mol% CO, 6.7 mol% CO2, and 33.2 mol% H2O in H2. The catalysts were characterized with several techniques, including X-ray diffraction (XRD), CO chemisorption, temperature-programmed reduction (TPR) with H2, temperature-programmed oxidation (TPO), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and bright-field transmission electron microscopy (TEM). Among the supported Pt catalysts tested, Pt/Ce0.4Zr0.6O2 showed the highest WGS activity in all temperature ranges. An improvement in the WGS activity was observed when CeO x was added with Pt on Ce x Zr1−x O2 supports (x = 0.05 and 0.2) due to intimate contact between Pt and CeO x species. Based on CO chemisorptions and TPR profiles, it has been found that the interaction between Pt species and surface ceria-zirconia species is beneficial to the WGS reaction. A gradual decrease in the catalytic activity with time-on-stream was found over Pt and Pt–CeO x catalysts supported on Ce x Zr1−x O2, which can be explained by a decrease in the Pt dispersion. The participation of surface carbonate species on deactivation appeared to be minor because no improvement in the catalytic activity was found after the regeneration step where the aged catalyst was calcined in 10 mol% O2 in He at 773 K and subsequently reduced in H2 at 673 K. [Copyright &y& Elsevier]

Abstract: The gas-phase dehydration of glycerol was conducted over silica–alumina catalysts with different Si/Al molar ratios. For comparison, SiO2 and η-Al2O3 were also examined. A variety of techniques, X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed oxidation (TPO) with mass spectroscopy (MS), infrared spectroscopy (FT-IR) after the adsorption of pyridine or glycerol, solid-state 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MAS/NMR) spectroscopy, Raman spectroscopy, and CHNS analysis, were employed to characterize the catalysts. The initial glycerol conversion at 315°C was strongly dependent on the total amount of acid sites over the silica–aluminas. The acrolein yield was proportional to the concentration of the Brønsted acid sites, whereas the 1-hydroxyacetone yield was proportional to the concentration of the Lewis acid sites. Among the tested catalysts, Si0.8Al0.2O x showed the highest acrolein selectivity during the initial 2h of the reaction. As long as the molar ratio between water and glycerol was in the range 2–11, the acrolein selectivity increased significantly with the water content of the feed. [Copyright &y& Elsevier]

Abstract: The gas-phase dehydration of glycerol was conducted over various H-zeolites, viz. H-ferrierite, H-β, H-ZSM-5, H-Y and H-mordenite with various SiO2/Al2O3 ratios. For comparison, γ-Al2O3 and silica-alumina were also examined. Several characterization techniques: X-ray diffraction (XRD), the temperature-programmed desorption of ammonia (NH3-TPD), the temperature-programmed desorption of water (H2O-TPD), temperature-programmed oxidation (TPO) with mass spectroscopy and CHNS analysis were employed to characterize the catalysts. The initial glycerol conversion at 315°C decreased in the following order: silica-alumina>H-β (25)>H-β (27)>γ-Al2O3 >H-mordenite (20)>H-ferrierite (55)>H-ferrierite (20)>H-ZSM-5 (23)∼H-β (350)>H-β (38)∼H-Y (5.1). H-ferrierite (55) showed the highest selectivity to acrolein at 315°C among the tested catalysts. The glycerol conversion over the solid acid catalysts was strongly dependent on their external surface area. In the case of the H-zeolites, most of the micropores were filled with carbon sources at the initial stage of this reaction. As long as the molar ratio between water and glycerol was in the range from 2 to 11, there was only a small change in the glycerol conversion, while the acrolein selectivity increased noticeably with increasing water content in the feed. The glycerol conversion and acrolein selectivity increased with increasing reaction temperature from 290°C to 340°C over H-ferrierite (55). The glycerol conversion and acrolein selectivity also increased with increasing contact time (W/F glycerol) which is defined as the ratio between the catalyst''s weight (W) and the molar flow rate of glycerol (F glycerol). [Copyright &y& Elsevier]