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We examined the effect of the particle size of gold on steam reforming of methanol over Au/CeO2-ZrO2 catalysts. Gold was loaded onto CeO2-ZrO2 through deposition-precipitation. The average particle size (2-12 nm) of the gold was controlled by thermal reduction under H2 at various temperatures and by chemical reduction with various reducing agents. The catalytic activity decreased significantly with increasing particle size of the gold. The turnover frequency at the interface between gold and a support appeared to be independent of particle size in the range 2-5 nm, which implies that the perimeter of the particle may be the active site for this reaction. Methanol adsorption and conversion over these catalysts were also investigated with in-situ diffuse reflectance infrared Fourier transform spectroscopy. Analytical results for various adsorbed intermediate species during methanol conversion suggests that transformation of methoxy species is facilitated by use of smaller gold particles.

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 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: 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]

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]

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]

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]

The preferential oxidation of CO (CO-PROX) under excess hydrogen over Au/MO x /Al 2 O 3 (M = La, Ce, and Mg) catalysts was investigated. All catalysts were prepared by a deposition-precipitation method with urea and characterized with inductively coupled plasma-atomic emission spectroscopy, N 2 physisorption, temperature-programmed reduction, X-ray diffraction, transmission electron microscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy. The catalytic activity of the supported gold catalysts was found to be dependent on the promoter, and decreased in the order: Au/La 2 O 3 /Al 2 O 3 > Au/CeO 2 /Al 2 O 3 > Au/MgO/Al 2 O 3 > Au/Al 2 O 3 . The catalytic activity of the Au/La 2 O 3 /Al 2 O 3 catalyst depended on the pretreatment conditions, i.e., reduction with aqueous NaBH 4 , thermal reduction with H 2 , and calcination with O 2 . This indicates that the oxidation state of gold is an important factor in the activity of the catalyst, and that metallic gold is more suitable than its oxidized form for this reaction. XPS results revealed that the treatment with aqueous NaBH 4 resulted in more negative charge in gold particles than that of conventional thermal reduction under H 2 . Smaller gold particles appeared to be favorable for the low-temperature CO-PROX activity of the Au/La 2 O 3 /Al 2 O 3 catalysts, which showed stable CO-PROX performance, even in the presence of CO 2 . [ABSTRACT FROM AUTHOR]

Abstract: We propose an activation method to control Ru particle size in supported Ru catalysts, viz. commercial Ru/Al2O3 and home-made Ru/SiO2, in order to increase the catalytic activity for the preferential CO oxidation (PROX). Ru particle size is controlled by adjusting pre-treatment conditions and it affects the catalytic activity for the PROX over supported Ru catalysts. Several measurements: inductively coupled plasma-atomic emission spectroscopy (ICP-AES), bright-field transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS), CO chemisorption, and O2 chemisorption were conducted to characterize the catalysts. The co-presence of H2 and O2 is essential for controlling the Ru particle size accurately. The PROX activity especially at low temperatures increases with increasing particle size of Ru, which seems to be closely related to the adsorption behavior of O2 on Ru surface. [Copyright &y& Elsevier]

• Rotary kiln reactor with alumina ball was used for pyrolysis of organosolv lignin. • Char agglomeration/foaming did not occur during continuous pyrolysis. • Rotary kiln reactor produced higher yield of organic phase oil. • Ni loaded biochar is a promising catalyst for gasification of plastics. • Ni/Fixed bed char showed the highest H 2 generation for HDPE gasification. In the pyrolysis of lignin, lignin tends to agglomerate during the feeding stage, and the char produced can expand easily to form foam that prevents continuous operation. To solve this problem, a new bench-scale rotary kiln reactor with alumina balls was used for the pyrolysis of organosolv lignin. Also, a bench-scale fixed-bed reactor was used as a reference reactor to gain an insight on the pyrolysis phenomena from rotary kiln reactor. Compared to the fixed bed reactor, the rotary kiln reactor resulted in a higher yield of organic phase oil with high selectivity to monomeric phenolic compounds. Moreover, a larger amount of CO 2 was obtained from the rotary kiln reactor, which strongly suggests that decarboxylation is main deoxygenation path. Furthermore, a char without agglomeration and foaming inside the reactor was generated from the rotary kiln reactor. The catalytic properties of the chars produced from both reactors with nickel impregnation were tested for the gasification of high-density polyethylene to produce H 2. Among the four different catalysts (Ni/Rotary Kiln char, Ni/Fixed Bed char, Ni/Al 2 O 3 , Ni/Activated carbon) tested, the Ni/Fixed Bed char exhibited the highest yield of H 2 (~two times higher H 2 generation) from the gasification process of high-density polyethylene. X-ray photoelectron spectroscopy and scanning electron microscopy offers that the high dispersion/distribution of Ni occurred when the fixed bed char was used as a support. All experimental findings from this study significantly suggest that Ni supported on char could be an economically viable catalyst for producing H 2 from gasification of high-density polyethylene. [ABSTRACT FROM AUTHOR]