Active Methanation Catalysts Research Articles

Bimetallic Ni-Based Catalysts for CO2 Methanation: A Review.

CO2 methanation has recently emerged as a process that targets the reduction in anthropogenic CO2 emissions, via the conversion of CO2 captured from point and mobile sources, as well as H2 produced from renewables into CH4. Ni, among the early transition metals, as well as Ru and Rh, among the noble metals, have been known to be among the most active methanation catalysts, with Ni being favoured due to its low cost and high natural abundance. However, insufficient low-temperature activity, low dispersion and reducibility, as well as nanoparticle sintering are some of the main drawbacks when using Ni-based catalysts. Such problems can be partly overcome via the introduction of a second transition metal (e.g., Fe, Co) or a noble metal (e.g., Ru, Rh, Pt, Pd and Re) in Ni-based catalysts. Through Ni-M alloy formation, or the intricate synergy between two adjacent metallic phases, new high-performing and low-cost methanation catalysts can be obtained. This review summarizes and critically discusses recent progress made in the field of bimetallic Ni-M (M = Fe, Co, Cu, Ru, Rh, Pt, Pd, Re)-based catalyst development for the CO2 methanation reaction.

Mechanistic assessment of dual function materials, composed of Ru-Ni, Na2O/Al2O3 and Pt-Ni, Na2O/Al2O3, for CO2 capture and methanation by in-situ DRIFTS

Recently, different Dual Function Materials (DFM) that capture CO2 from a power plant flue gas stream with catalytic conversion to CH4 have been developed. DFMs are composed of an alkaline adsorbent and an active methanation catalyst supported on a high surface area carrier. Among the different DFMs studied, relatively inexpensive 10%Ni,6.1%“Na2O”/Al2O3 DFM (NiDFM) reported high methanation activity. However, due to rapid oxidation of Ni active sites, it is not suitable for O2-containing applications. The presence of small amounts of Ru or Pt in combination with Ni promote the reduction of NiOx rendering it active towards CO2 methanation upon the addtion of H2. Therefore, mechanistic insights of the presence of Ru or Pt with Ni DFMs during CO2 capture was investigated by in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) under both non-oxidizing and oxidizing conditions. Under both, O2 and O2-free conditions, at 320 °C, Pt dissociates CO2 to form a CO-Pt species providing a new CO2 adsorption site on the DFM surface. The greatest NiO reduction occurrs for the 1%Ru,10%Ni,6.1%“Na2O”/Al2O3 (RuNiDFM) with a lesser effect for 1%Pt,10%Ni,6.1%“Na2O”/Al2O3 (PtNiDFM). Also, RuNiDFM gives the the best performance methanation.

Unveiling the structural transitions during activation of a CO2 methanation catalyst Ru0/ZrO2 synthesised from a MOF precursor

Carbon Capture, Utilisation and Storage (CCUS) technologies are utilised to minimise net CO2 emissions and hence mitigate the impact of anthropogenic emissions on the global climate. One example of CO2 utilisation is the production of carbon-neutral methane fuel via catalytic CO2 reduction with H2 (methanation). Thermal activation of a metal impregnated metal-organic framework (MOF), 1 wt%Ru/UiO-66 in the presence of H2 and CO2 provides in situ synthesis of a highly active methanation catalyst: H2 promotes the formation of Ru0 nanoparticles, and CO2 behaves as a mild oxidant to remove framework carbon and promote ZrO2 crystallisation. The nature of the active MOF-derived Ru0/ZrO2 catalyst was studied by PXRD, TEM, and XAS, and the evolution of the parent 1 wt%Ru/UiO-66 during thermal activation monitored in operando by synchrotron PXRD. The Ru impregnated Zr-based MOF collapses on heating in H2 and CO2 to form an amorphous C and Zr containing phase that subsequently crystallises as tetragonal (t-) ZrO2 nanoparticles. These t-ZrO2 nanoparticles undergo a subsequent phase transition to the more stable monoclinic (m-) ZrO2 polymorph. In situ activation of Ru/UiO-66 generates a highly active catalyst for CO2 methanation by transforming the MOF precursor into a (carbon-free) crystalline t-ZrO2 support that stabilises highly dispersed metallic Ru nanoparticles. This insight may guide the rational design of future MOF-derived catalysts.

An active methanation catalyst prepared from PdZr alloys

Highly active methanation catalyst for the reaction of carbon monoxide and hydrogen to produce methane was prepared in situ from an amorphous Pd 35Zr 65 alloy. Its turnover frequency was greater than that for the most active methanation catalyst as ever known. The activity of the catalyst was compared with those of the crystalline Pd xZr 1−x (x=0−1) alloys and Pd(Zr,Si) alloys. The results showed that the active species, prepared in situ from amorphous Pd 35Zr 65 alloy, is a unknown complex oxide of Pd and Zr, in which palladium exists in the oxidation state under the highly reducing reaction condition. But, Pd-base catalysts containing Si as additive did not form the active species like the complex oxide of Pd and Zr during the reaction and therefore deactivated.

AN ACTIVE METHANATION CATALYST PREPARED FROM AN AMORPHOUS Pd35Zr65 ALLOY

Abstract Highly active methanation catalyst was prepared in situ from an amorphous Pd35Zr65 alloy. In the reaction at 260°C, 1 atm, the catalytic avtivity remarkably increaed with time, showing about hundred fold enhancement, compared with the initial value, at the steady state attained in 60 h. Thr turnover frequency was greater than or comparable to those for the most active methanation catalysts as ever known.