Dry reforming of toluene over nickel based hydrotalcite catalysts : effect of lanthanum and cerium doping

Abstract

Three series of catalysts were synthesized by hydrotalcite route and calcined at 800°C. These series are NixMg6-xAl2, NixMg6-xAl1.8La0.2 and NixMg6-xAl1.8Ce0.2 ( With 0<x<6). The characterisation of the catalysts was done before and after their calcination. The characterization techniques used are X-ray Diffraction (XRD), Thermogravimetric and Differential Thermal Analysis (TG-DTA), Nitrogen Adsorption/ Desorption, Temperature Programmed Reduction (H2-TPR), Oxidation (TPO) and Desorption (CO2- TPD). The catalytic activities were tested in the dry reforming of toluene In addition, the catalytic activities were compared to evaluate the effect of lanthanum and ceria doping on the performance of catalysts in dry reforming of toluene. TG-DTA results showed that that the higher the nickel content in the hydrotalcites created a more crystalline structure and decreased the thermal stability. Similarly, the addition of promoters also decreased the thermal stability of hydrotalcites. TPR results showed that higher nickel content made it easier to reduce the catalysts at the temperatures of the experiment. Moreover, ceria doping had the same effect, but lanthanum doping made the reduction difficult. The CO2- TPD results showed that nickel and lanthanum decreased the basicity whereas the ceria increased the basicity. These characterisation results helped in the interpretation of the performance of catalyst during dry reforming of toluene. After test, catalysts were characterized by TPO and XRD. They showed carbon deposition on all catalyst surfaces. Based on the catalytic test results along with H2/CO ratios and carbon assessment of all catalysts, three catalysts were selected to be tested for their stability for 10h on stream. The aim was to investigate their deactivation due to sintering or carbon deposition. The Ni2Al1.8Ce0.2 had the best performance among all other catalysts.