Ni and RhNi catalysts supported on Zeolites L for hydrogen and syngas production by biogas reforming processes

This study examined the use of three different Zeolites L as catalyst support for biogas valorisation – a renewable resource – through reforming processes. These aluminosilicates are characterised by their high surface areas, affinity for CO2, and thermal stability, which makes them an interesting and promising support for reforming reactions at high temperature. Three nickel monometallic and their homologous rhodium–nickel bimetallic catalysts were prepared by the incipient wetness impregnation method for each type of Zeolite L. Significant physicochemical differences between the Zeolites L and catalysts were noticed by the characterisation using scanning electron microscope (SEM), transmission electron microscope (TEM), inductively coupled plasma atomic emission spectrometry (ICP-AES), H2 chemisorption, N2 physisorption, temperature programmed reduction (TPR) X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The catalysts were tested in dry reforming (DR), steam reforming (SR) with steam to carbon (S/C) ratio of 1.0 and 2.0; oxidative reforming (OR) at O2/CH4 = 0.25; and tri-reforming (TR) with S/C ratio of 1.0 and O2/CH4 = 0.25. For all the experiments, a synthetic biogas, which consisted of 60% CH4 and 40% CO2 (vol.), was fed to a fixed bed reactor system at 1073 K and atmospheric pressure. The same experimental conditions and reactions were studied in previous works of the authors, in which γ-Al2O3 was used as a catalyst support. Thus, this work allows comparing the achieved activities by the tested catalysts supported on those different supports. Among the processes studied, for the biogas SR at S/C = 1.0 and TR processes, H2/CO ratios near to 2.0 were obtained, which is an appropriate ratio for the Fischer–Tropsch synthesis (FTS). In the case of the catalysts tested, the Rhodium (Rh) incorporation improved their activity. Rh Ni catalyst based on Zeolite L (30–60 nm) is the most active catalyst for hydrogen generation.