Toluene steam reforming properties of CaO based synthetic sorbents for biomass gasification process

Biomass gasification process generates undesired Topping Atmosphere Residue (TAR), removable by catalytic steam reforming. The use of a CO₂-sorbent powder inside the reactor bed can minimize the content of carbon dioxide and carbon monoxide by enhancing the water gas shift (WGS) reaction, offering a fuel gas rich of H₂. The present study addresses the practical feasibility of such concepts, using toluene as a representative TAR and a hybrid compound Ni/CaO–Ca₁₂Al₁₄O₃₃ as reactor bed material, simultaneously acting as reforming catalyst and CO₂ sorbent. In fact, the CaO is the effective sorbent, whereas the Ca₁₂Al₁₄O₃₃ is a support for both the CaO and the active metallic Ni particles. A different synthesis route with respect to the literature has been developed for the production of the Ni/CaO–Ca₁₂Al₁₄O₃₃ and a total of three different bed reactor powders have been tested and compared: (i) a mixture of olivine and commercial nickel catalyst, (ii) a mixture of CaO–Ca₁₂Al₁₄O₃₃ and commercial nickel catalyst, and (iii) the Ni/CaO–Ca₁₂Al₁₄O₃₃ combined catalyst and sorbent. The best performances have been observed in the latter, with toluene conversion close to 99%, and the volume fraction of hydrogen in the gas over 95%. During multi-cycle tests, the synthetic Ni/CaO–Ca₁₂Al₁₄O₃₃ combined catalyst and sorbent exhibited superior resistance to carbon deposition and stability in toluene conversion compared to the other bed materials that suffer from decreased conversion efficiency after few cycles.