| The current study deals with the design and development of catalysts for the CO2 reforming of biogas in order to produce bio-renewable hydrogen. Accordingly, a series of mixed oxide supports based on MOx-Al 2O3 (where M = Mg, Ca, La) were prepared using a 1:3 molar oxide ratio and a surfactant-assisted route. A nominal 15 wt. % Ni was impregnated over the aforementioned calcined supports using a standard wet impregnation method. In order to investigate the effect of cobalt on the nickel-supported catalysts, a series of Ni-Co bimetallic catalysts were prepared by adapting simultaneous and step-wise wet-impregnation strategies. In the step-wise scheme, Co was impregnated after Ni, while in the simultaneous scheme, both the metallic elements, Ni and Co, were impregnated simultaneously. The catalysts were screened under realistic operation conditions, employing a feed with a CH4/CO 2 ratio = 1.25, 100 ppmv H2S, a 900 °C temperature, 1 atm. pressure, and WHSV = 18750 ml/g(cat.).h. Among the various catalyst formulations screened, the catalysts prepared using monometallic Ni active species fared well. Also, it was noted that the bimetallic Ni-Co catalysts obtained using a simultaneous impregnation route performed better than stepwise counterparts. A thorough physico-chemical characterization of the fresh catalysts was undertaken by means of N2-physisorption, H2 chemisorption, inductively coupled plasma mass spectrometry (ICP-MS) and temperature programming reduction (TPR). From the screening results, the 15Ni/CaO-Al2O3 catalyst was found to exhibit comparatively higher activity and better stability, and it was, therefore, chosen for further parametric studies. The various parametric studies performed over the above chosen catalysts are: surfactant/metal ratio effect, CH4-to-CO 2 ratio effect, H2S effect, and temperature. In order to test the effect of the surfactant/metal molar ratio on the catalyst's performance, a series of CaO-Al2O3 supports were prepared using a surfactant-assisted route and different CTAB/metal molar ratios, i.e., 0.3, 0.5, and 1.25. The methane effect was studied by varying the CH4/CO2 ratio from 1 to 1.25, while the H2S effect was studied using H2 S-free biogas and bio-gas containing 100 ppmv H2S; finally, the effect of temperature was studied by varying the temperature, viz., 800 °C and 900 °C. A practical structure activity relation (SAR) was developed by correlating the activity results with their inherent structural and physico-chemical characteristics. SARs helped explain the significant difference in activity among the catalysts containing monometallic and bimetallic species and among the bimetallic species impregnated in two different ways: simultaneous and stepwise. SARs also helped to identify the effect of a different amount of surfactant on the best chosen catalytic activity. High surface area, high pore volume/surface area, high metallic surface area, and high reducibility are necessary for the CO2 reforming of biogas using sulphur tolerance catalysts as developed in this research. |
