Reaction mechanism of naphtha steam reforming on nickel-based catalysts, and FTIR spectroscopy with CO adsorption to elucidate real active sites

摘要

To improve the understanding of the hydrocarbon steam reforming reaction mechanism and the nature of the active sites, different nickel-based catalysts have been synthesized and studied under several reaction conditions. Catalysts from hydrotalcite precursors show better activity and higher coking resistance than traditionally prepared samples. Furthermore, introducing additives (Ce, Li or Co) in the hydrotalcite structure produces no blockage of the nickel active sites. Different structural and physical-chemical properties have been analyzed by XRD, TPR, BET and elemental analysis. FTIR spectroscopy with CO adsorption reveals interesting catalyst structure-catalytic behavior relationships; oxygen release through the catalyst surface is key parameter to improve steam reforming activity and coking resistance; and, highly unsaturated Ni surface atoms located on the metal-support interphase are relevant structures to the catalysis and most active sites for the steam reforming reaction. Steam reforming reaction proposed sequence involves: 1) hydrocarbon preferably activation on active Ni surface sites and steam preferred activation on basic support surface sites, 2) oxygen spill-over from the support to the metal phase, and 3) reaction between carbon and oxygen species occurring on the metal-support interphase.