Rate Enhancement Effects of Steam Reforming of Methane over Dynamic Ruthenium Catalysts



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Methane (CH4) is the second-most abundant greenhouse gas with a warming potential 25 times as great as carbon dioxide. Short-term action plans directed toward diminishing the effects of global warming should therefore include the mitigation of methane emissions. The direct capture of distributed CH4 emitted by relatively intractable sources like livestock for subsequent large-scale industrial processing faces severe economic challenges. On-site treatment of CH4 via transition-metal catalyzed steam reforming (SMR) in mobile, dynamically operated modular reactors can overcome the economic barriers of capturing stranded CH4. Existing kinetic studies of SMR over transition metal surfaces identified two competing surface phenomena: CH4 activation and CO* formation. The coupled nature of these two surface reactions limits the maximum realizable activity from static catalysts to the Sabatier optimum. In this work, decoupling of the competing elementary reactions over stepped Ruthenium (Ru) is attempted by modulating the chemisorption energy of the surface carbon intermediate (ΔEC). Brönsted-Evans-Polanyi (BEP) and scaling relationships were used to model the energy dependence of transition states and other surface intermediates, respectively, on ΔEC. Catalytic dynamics were simulated with a lumped kinetic model. ΔEC was oscillated as a square wave about two Ru basis energies with amplitudes of 0.1 eV and 1 eV over a broad range of frequencies. A band of frequencies (105 Hz - 109 Hz) corresponding to maximum enhancement in the time-averaged rate of SMR is observed.



Dynamic catalysis, Methane steam reforming, Heterogeneous catalysis