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• 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]

• The effect of promoter was evaluated for CO and CO 2 methanation. • Mn, Ce, Mg, V, and Zr are beneficial for both CO and CO 2 methanation activity. • CO 2 methanation is related to the Ni dispersion and relevant CO 2 adsorption. • Ni-V/Al@Al 2 O 3 with the highest Ni dispersion is the best for CO methanation. • The promotional effect of Mn is remarkable for both CO and CO 2 methanation. Effects of metal promoter on CO and CO 2 methanation were examined over Ni-M (M = Mn, Ce, Zr, Mg, K, Zn, or V)/Al@Al 2 O 3 catalysts prepared by the co-impregnation method. Ni-M (M = Mn, Ce, or Zr)/γ-Al 2 O 3 catalysts were also investigated for comparison. The prepared catalysts were characterized with a variety of techniques such as N 2 physisorption, CO 2 chemisorption, H 2 chemisorption, temperature-programmed reduction with H 2 (H 2 -TPR), temperature-programmed desorption of CO 2 (CO 2 -TPD), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Among different promoters, Mn, Ce, Mg, V, and Zr are beneficial to enhance both CO and CO 2 methanation activity due to the improvement of the Ni dispersion. The Ni-V/Al@Al 2 O 3 catalyst performs the highest CO methanation activity due to the largest Ni sites. However, it is not the best one for CO 2 methanation among tested catalysts because of the much decrease in CO 2 adsorption capacity. The promotional effect of Mn is the most remarkable for both CO and CO 2 methanation. On the other hand, the negative effect of K and Zn was observed on both CO and CO 2 methanation by the small number of active Ni sites and the decrease in the amount of basic sites. The CO 2 methanation mechanism over Ni-Mn/Al@Al 2 O 3 catalyst is elucidated by the transform route: adsorbed carbonate species – formate species – methane under hydrogenation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ru/Al@γ-Al 2 O 3 catalysts were applied to preferential CO oxidation in H 2 (PROX). • The thickness of Al 2 O 3 layer in Al@ Al 2 O 3 is an important factor. • The good PROX performance over a wide reaction temperature was achieved. • Ru nanoparticles with weak adsorption of CO are plausible for PROX. The thermal-conducting support is highly desirable for endothermic and exothermic reactions as long as highly dispersed active sites can be maintained. The core-shell Al@Al 2 O 3 supports with different aluminum (Al) contents were prepared from Al particle by controlling the reaction time during hydrothermal surface oxidation and applied as a support to the supported Ru catalysts for preferential CO oxidation in H 2 (PROX). The prepared catalysts were characterized by N 2 -physisorption, X-ray diffraction, CO chemisorption, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), in situ diffuse reflectance infrared Fourier transform spectroscopy after CO adsorption (CO-DRIFTS), and temperature-programmed desorption of ammonia (NH 3 -TPD) and ethanol (ethanol-TPD). The catalytic activity was dependent on the Al content in the Al@Al 2 O 3 support. The most active Ru/Al@γ-Al 2 O 3 catalyst oxidized CO selectively in H 2 over a wide reaction temperature. The surface property of the outermost exterior alumina layer in the Al@γ-Al 2 O 3 support, determined with ethanol TPD, was beneficial for formation of Ru nanoparticles with weak adsorption of CO, probed with CO-DRIFTS, results in the high catalytic performance for PROX. [ABSTRACT FROM AUTHOR]

Various Ni catalysts supported on γ-Al₂O₃ were prepared by a wet impregnation (WI) method and deposition-precipitation (DP) method with different precipitants and applied to CO and CO₂ methanation. The prepared catalysts were characterized by various techniques including nitrogen physisorption, X-ray diffraction (XRD), temperature-programmed reduction with H₂ (H₂-TPR), H₂ chemisorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Irrespective of kinds of precipitant, the Ni/γ-Al₂O₃ catalysts prepared with a DP method showed a remarkable enhanced catalytic performance in CO and CO₂ methanation compared with the Ni/γ-Al₂O₃ catalyst prepared with a WI method owing to the higher catalytic active surface area (CASA). In the case of Ni/γ-Al₂O₃ catalysts prepared with a DP method, the high calcination temperatures are not favorable for the high catalytic activity due to the decreased reduction degree of Ni oxide species and CASA. The reduction degree of Ni oxide species can be increased with reduction temperature. However, the higher reduction temperature above 500 °C is not desirable to achieve the high catalytic activity because of the decreased CASA. The selective CO methanation was also accomplished at lower temperatures over the Ni/γ-Al₂O₃ catalyst prepared with a DP method than over the Ni/γ-Al₂O₃ catalyst prepared with a WI method.