CO2 Methanation on Supported Rh Nanoparticles: The combined Effect of Support Oxygen Storage Capacity and Rh Particle Size

Abstract

CO2 hydrogenation toward methane, a reaction of high environmental and sustainable energy importance, was investigated at 200–600 °C and H2/CO2 = 4/1, over Rh nanoparticles dispersed on supports with different oxygen storage capacity characteristics (γ-Al2O3, alumina-ceria-zirconia, and ceria-zirconia). The effects of the support OSC and Rh particle size on reaction behavior under both integral and differential conditions were investigated, to elucidate the combined role of these crucial catalyst design parameters on methanation efficiency. A volcano-type variation of methanation turnover frequency was found in respect to support OSC; Rh/ACZ, with intermediate OSC, was the optimal catalyst. The structure sensitivity of the reaction was found to be a combined function of support OSC and Rh particle size: For Rh/γ-Al2O3 (lack of OSC) methanation was strongly favored on small particles—the opposite for Rh/CZ (high OSC). The findings are promising for rational design and optimization of CO2 methanation catalysts by tailoring the aforementioned characteristics.

Bimetallic Ni-Based Catalysts for CO2 Methanation: A Review

“…Y and Zr, for example, are mostly used as dopants to modify the lattice of the metal oxide support and enhance its defect chemistry. Zr is used to stabilize the CeO 2 structure and enhance its oxygen vacancies population (i.e., oxygen storage capacity, OSC) [19], while Y can generate oxygen vacancies in ZrO 2 -based supports [34,35]. Mn mostly forms MnO x phases that increase the catalyst basicity and favour CO 2 chemisorption.…”

“…Mn mostly forms MnO x phases that increase the catalyst basicity and favour CO 2 chemisorption. All these modifications on the support's properties can lead to an increase in CO 2 activation and, thus, Mn, Ce, Zr and Y are often regarded as efficient promoters in CO 2 methanation [19,[34][35][36].…”

“…Although noble metals are significantly pricier than transition metals, they can provide significant advantages regarding the CO 2 methanation reaction, due to their excellent low-temperature activity, as well as their high reducibility and stability once oxidized [18,19,[91][92][93]. The combination of Ni with a noble metal aims to transfer some of these properties into Ni-based catalysts, without the need for the use of a high noble metal loading [33].…”

“…Rhodium (Rh) is one of the most expensive noble metals and it is known to be highly active for CO 2 methanation at low temperatures, even when used under very low loadings [ 19 , 113 ]. However, its presence in bimetallic Ni-Rh catalysts does not always lead to a desirable activity increase, especially when taking into consideration the increased cost of the catalytically active material.…”

“…Besides Ni, Ru and Rh noble metals have been extensively studied as active metallic phases in CO 2 methanation and they usually achieve a much higher activity at low temperatures [ 18 , 19 ]. Since CH 4 is thermodynamically favoured over other CO 2 hydrogenation products such as CO, at low temperatures, CH 4 selectivity can be significantly higher when using noble metal catalysts [ 7 ].…”