Search

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]

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]

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: 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]

In this study, unique core-shell aluminate spinel supports, Al@MAl2O4 (M = Zn, Mg, or Mn), were obtained by simple hydrothermal surface oxidation and were applied to the preparation of supported Ni catalysts for CO2 methanation. For comparison, CO methanation was also evaluated using the same catalysts. The prepared catalysts were characterized with a variety of techniques, including N2 physisorption, CO2 chemisorption, H2 chemisorption, temperature-programmed reduction with H2, temperature-programmed desorption of CO2, X-ray diffraction, high-resolution transmission electron microscopy, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The combination of supports with core-shell spinel structures and Ni doping with a deposition–precipitation method created outstanding catalytic performance of the Ni catalysts supported on Al@MgAl2O4 and Al@MnAl2O4 due to improved dispersion of Ni nanoparticles and creation of moderate basic sites with suitable strength. Good stability of Ni/Al@MnAl2O4 catalyst was also confirmed in the study. [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]

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]

• Core–shell Al@Al2O3 was used as the support in supported Ni catalysts. • The Al@Al2O3 is better than γ-Al2O3 to develop a highly efficient Ni-based catalyst. • The deposition–precipitation method outperforms the wet impregnation method. • Higher Ni dispersion resulted in better catalytic performance for CO methanation. • The higher density of medium basic sites increases the CO 2 methanation activity. Core–shell Al@Al 2 O 3 , which was obtained by hydrothermal surface oxidation of Al metal particles, was used as the support in supported Ni catalysts for CO and CO 2 methanation. The core–shell micro-structured support (Al@Al 2 O 3) helped develop a highly efficient Ni-based catalyst compared with conventional γ-Al 2 O 3 for these reactions. Moreover, the deposition–precipitation method was shown to outperform the wet impregnation method in the preparation of the active supported Ni catalysts. The catalysts were characterized using various techniques, namely, N 2 physisorption, H 2 chemisorption, CO 2 chemisorption, temperature-programmed reduction with H 2 , temperature-programmed desorption after CO 2 adsorption, X-ray diffraction, inductively coupled plasma-atomic emission spectroscopy, high-resolution transmission electron microscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. Higher Ni dispersion when using Al@Al 2 O 3 as the support and the deposition–precipitation method resulted in better catalytic performance for CO methanation. Furthermore, the higher density of medium basic sites and enhanced CO 2 adsorption capacity observed for Ni/Al@Al 2 O 3 helped increase catalytic activity for CO 2 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]

CO and CO 2 methanation over Na/Ni/SiO 2 and Na/Ni/CeO 2 catalysts with different Na contents (0, 0.1, and 1 wt%) were studied. N 2 physisorption, H 2 chemisorption, temperature-programmed reduction with H 2 , CO 2 chemisorption, temperature-programmed desorption of CO 2 , temperature-programmed oxidation, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy were employed to characterize the catalysts. Even just 0.1 wt% Na was observed to have a negative effect on CO methanation for the Na/Ni/SiO 2 and Na/Ni/CeO 2 catalysts owing to surface blockage of the Ni metal. The negative effect of Na on CO 2 methanation was also observed for the Na/Ni/CeO 2 catalysts. Conversely, Na exhibited a positive effect upon CO 2 methanation over the Na/Ni/SiO 2 catalysts. The different effect of Na on CO 2 methanation is closely related to the amount of CO 2 chemisorbed on the catalysts. Stable catalytic activity for CO and CO 2 methanation was observed for Ni/SiO 2 , Na/Ni/SiO 2 , and Ni/CeO 2 . However, the Na/Ni/CeO 2 catalyst was deactivated during CO methanation owing to coke formation following olefin production. However, this catalyst was stable for CO 2 methanation. [ABSTRACT FROM AUTHOR]

CO and CO 2 methanation was investigated over Ni catalysts supported on different supports such as γ-Al 2 O 3 , SiO 2 , TiO 2 , CeO 2 , and ZrO 2 . Among them, Ni/CeO 2 was determined to be the most active for CO and CO 2 methanation. These catalytic activities increased with increasing surface area of CeO 2 . To increase the specific catalytic activity for CO and CO 2 methanation, various Ni-CeO 2 catalysts with different Ni contents were prepared using co-precipitation method. The optimum Ni content was determined for both reactions. The prepared catalysts were characterized with inductively coupled plasma-atomic emission spectroscopy, N 2 physisorption, temperature-programmed reduction, temperature-programmed desorption, and X-ray diffraction. The high Ni dispersion and strong CO 2 adsorption appeared to be responsible for the high catalytic activity for CO and CO 2 methanation. This Ni-CeO 2 can be applied to the low-temperature CO and CO 2 methanation reactor to achieve high single-pass conversions of CO and CO 2 . [ABSTRACT FROM AUTHOR]

Abstract: The effect of various Mo catalyst supports, i.e., γ-Al2O3, SiO2, SiO2–Al2O3, ZrO2, yttria-stabilized zirconia (YSZ), CeO2, and TiO2, on CO hydrogenation in the presence of H2S was examined. At 5wt.% Mo loading, Mo/ZrO2 was determined to be the most active catalyst for this reaction; its activity was dependent on the number of active sites, as determined via NO chemisorption. Raman spectroscopy revealed that MoO3 transforms into MoS2 during the reaction. [Copyright &y& Elsevier]