(336i) Direct, Single-Pass Thermocatalytic Upgrading of Biogas and Landfill Gas into Renewable Natural Gas over the Ultra-Low Loading Ru/?-Al2O3 Catalyst

Direct,
single-pass thermocatalytic upgrading of biogas and landfill gas into renewable
natural gas over the ultra-low loading Ru/g-Al₂O₃
catalyst

Yichen Zhuang and David Simakov

Department of Chemical Engineering,
University of Waterloo, Waterloo, ON N2L 3G1, Canada

Converting CO₂ into
synthetic renewable fuels is an attractive pathway to decrease CO₂
emissions and to reduce our dependence on fossil fuels. Thermocatalytic
hydrogenation provides advantages of fast reaction rates and high conversion
efficiencies (as compared to electro-catalytic and photo-catalytic routes),
thus allowing for compact, high-throughput operation. One option is to convert
CO₂ into synthetic methane, so-called renewable natural gas (RNG)
via the Sabatier reaction (CO₂ + 4H₂ = CH₄ +
2H₂O). Water electrolysis using renewable or surplus electricity can
be used to provide a non-fossil source of H₂ required for the
reaction. There are multiple sources of concentrated CO₂-containing
streams including biogas and landfill gas (up to 50 mol% CO₂). It is
highly desirable to develop a technology that can convert such CO₂-rich
streams directly, without costly upstream CO₂ separation.

One of the most fundamental
challenges is the development of a catalyst, which is highly active, selective
to CH₄ formation, stable against coking, and low-cost at the same
time. The selectivity becomes a major challenge when a mixed feed (biogas or
landfill gas contain up to 50 mol% CH₄ in addition to CO₂)
is used instead of purified CO₂ feed. In this study, a highly
selective Ru-based catalyst with ultra-low Ru loadings (less than 0.5 wt%) is
reported. A series of catalysts with Ru loadings ranging from 0.05-0.5 wt% were
synthesized and evaluated for their catalytic activity in selective conversion
of CO₂ in the mixed CH₄/CO₂ feed. CO₂
conversions up to 80% were achieved with nearly complete selectivity to CH₄
generation (left plot in the figure below). Importantly, the catalysts showed
good stability, without any notable decline in performance over 60 hours on
stream at very high space velocity of GHSV = 90,000 1/h (right plot in the
figure below). A variety of analytical techniques were employed in order to
investigate the mechanism of the superior selectivity and activity, including
electron microscopy, thermal gravimetric analysis, temperature programmed
reaction, chemisorption, and X-ray photon spectroscopy. Our results point out
at the strong structure-activity relationship and the importance of the active
phase interaction with the support.