Nano-sized Ni/(CaO)x-(Al2O3)y catalysts for steam pre-reforming of ethane and propane in natural gas: The role of CaO/Al2O3 ratio to enhance conversion efficiency and resistance to coke formation

Abstract

Steam pre-reforming of natural gas was studied over of 31 wt% Ni/(CaO)x-(Al2O3)y catalysts at 400–550 °C, low steam to carbon molar ratio (1.5) and atmospheric pressure. Binary Calcium aluminate compounds with different molar ratio of CaO/Al2O3 = 3/1, 1/1, 1/2 and 1/6 were synthesized by a decomposition method. The obtained powders were employed as a support to prepare a series of mesoporous 31 wt% Ni/(CaO)x-(Al2O3)y catalysts by the deposition-precipitation method. The N2 adsorption/desorption, SEM, XRD, TPR, TPO and TPD techniques were used to characterize the obtained (CaO)x-(Al2O3)y supports and catalysts. Although the catalytic test was performed at a high gas hourly space velocity (GHSV = 1 × 105 1/h), all prepared catalysts provided around 100% of ethane and propane conversions at 500–550 °C. Variation in the catalytic activity was revealed at a much higher GHSV (2 × 105 1/h). The ethane and propane conversions were increased with increasing in the CaO/Al2O3 molar ratio up to 1/1 and the 31 wt% Ni/(CaO)x-(Al2O3)y catalyst showed the highest conversions. The CO2-TPD results indicated that the basicity of supports was strongly influenced by the CaO/Al2O3 molar ratio. Increasing the CaO/Al2O3 ratio resulted in a higher surface basicity and showed a positive effect on the coke suppression. The TPO and SEM of spent catalysts, after 60 h stability test, showed a plenty amount of coke formation on the 31 wt% Ni/CA6 catalyst, while a high resistance to carbon deposition was observed in the case of 31 wt% Ni/C3A catalyst.