Rice Husk Ash-Derived Ca-Mg-Modified Silicate as Support for Ni-Co for Hydrogen Production by Sorption-Enhanced Steam Reforming of Bioethanol

Abstract

A multipurpose catalyst made of nickel and cobalt supported on silicate-based material modified by Ca and Mg was developed and used in sorption-enhanced steam reforming of (bio)-ethanol (SESRE). In SESRE, steam reforming and CO2 conversion to carbonates occur together to yield clean hydrogen. The catalyst was designed using silica sourced from rice hull ash (RHA) by oxidation and, subsequently, Ni and Co were loaded by the wet-impregnation technique. Three catalysts, namely, Ni/Ca-Mg silicate, Co/Ca-Mg silicate, and Ni-Co/Ca-Mg silicate, were synthesized with different metal loadings (5–15% w/w), among which 10 %Ni-10% Co/Ca-Mg silicate was the most active and selective. Various characterization techniques were used to determine the physico-chemical properties of 10% NI-10% Co/Ca-Mg silicate. CO2-sorption capacity and adsorption breakthrough time were measured. An adsorption capacity of 7.4 mol CO2/kg sorbent and a breakthrough time of 58 min at T = 723 K were observed with hydrogen production at 88 mol %. The catalyst was evaluated and optimized using such parameters as temperature, S/C ratio, and space velocity. The catalyst was tested for its robustness and found to be stable for 10 cycles. 10% Ni-10% Co/Ca-Mg yielded the best hydrogen output under the optimized operating conditions.