CO2 Methanation Using Multimodal Ni/SiO2 Catalysts: Effect of Support Modification by MgO, CeO2, and La2O3

Abstract

Ni/oxide-SiO2 (oxide: MgO, CeO2­, La2O3, 10 wt.% target concentration) catalyst samples were prepared by successive impregnation of silica matrix, first with supplementary oxide, and then with Ni (10 wt.% target concentration). The silica matrix with multimodal pore structure was prepared by solvothermal method. The catalyst samples were structurally characterized by N2 adsorption-desorption, XRD, SEM/TEM, and functionally evaluated by temperature programmed reduction (TPR), and temperature programmed desorption of hydrogen (H2-TPD), or carbon dioxide (CO2-TPD). The addition of MgO and La2O3 leads to a better dispersion of Ni on the catalytic surface. Ni/LaSi and Ni/CeSi present a higher proportion of moderate strength basic sites for CO2 activation compared to Ni/Si, while Ni/MgSi lower. CO2 methanation was performed in the temperature range of 150–350 °C and at atmospheric pressure, all silica supported Ni catalysts showing good CO2 conversion and CH4 selectivity. The best catalytic activity was obtained for Ni/LaSi: CO2 conversion of 83% and methane selectivity of 98%, at temperatures as low as 250 °C. The used catalysts preserved the multimodal pore structure with approximately the same pore size for the low and medium mesopores. Except for Ni/CeSi, no particle sintering occurs, and no carbon deposition was observed for any of the tested catalysts.

Polymer-derived SiOC as support material for Ni-based catalysts: CO2 methanation performance and effect of support modification with La2O3

“…Since SiOC pyrolyzed at 600°C shows no activity in the H 2 -TPR itself, the peaks at 270, 311°C and 580°C in the sample containing 5 wt% Ni can be attributed to NiO particles with different reducibility. The additional peak at 580°C indicates the presence of a NiO species in stronger interaction with the support material, which leads to an increased stability against sintering of the active phase in this sample ( Mihet et al, 2021 ). Crystallite size determinations of the fresh and used catalyst in Table 1 confirm this observation as no significant crystallite growth occurred during catalytic reaction.…”

“…H 2 -TPR measurements provide information about the reducibility of the active phase but also on the strength of interactions between metal oxides and the support material. It is generally accepted that, since the reduction of NiO to Ni is a single step process (NiO + H 2 → Ni 0 +H 2 O), irregular shapes of hydrogen consumption peaks can be attributed to differences in the NiO-support interactions ( Branco et al, 2020 ; Mihet et al, 2021 ). The unmodified catalyst supported on polymer-derived SiOC pyrolyzed at 800°C ( Figure 4A ) shows a single H 2 consumption peak at 355°C.…”

“…In contrast to SiOC800, catalysts supported on SiOC600 contain only metallic nickel. This can be explained by different calcination conditions: While SiOC800-supported samples were calcined in air, catalysts based on SiOC600 were calcined in Ar atmosphere where the formation of NiO was suppressed ( Mihet et al, 2021 ). While the Ni phases can be clearly identified, most of the diffraction patterns do not show a La 2 O 3 reflex as this phase may be highly dispersed.…”

“…Some of the main drawbacks encountered in the use of Ni-based catalysts are the insufficient low-temperature activity, poor dispersion and reducibility of the catalyst particles, sintering and aggregation of the active phase. Several studies showed that La 2 O 3 can be an effective additive to avoid particle coalescence and sintering ( Zhi et al, 2011 ; Zhu et al, 2011 ; Mihet et al, 2021 ; Riani et al, 2021 ). Another simple and cost-effective solution to increase the stability of catalysts is the use of a support material with high thermal conductivity and thermal stability such as silicon carbide to dissipate the reaction heat ( Zhi et al, 2011 ; Zhang et al, 2013 ).…”

Metal-induced oxygen vacancies on Bi2WO6 for efficient CO2 photoreduction

“…In addition, BWO/0.1%Au also exhibits two extra adsorption peaks near 592 and 667°C. This indicates that partial CO 2 molecules are chemically strongly adsorbed on the surface of BWO in BWO/0.1%Au, which is beneficial to the further activation of CO 2 [41,42] .…”