The Preparation Of A Ni-CaO/Al₂O₃Sorption Complex Catalyst By Hydrothermal Precipitation Method And Application In ReSER Process

Reactive sorption enhanced reforming (ReSER) has been paid more attention because this process can improve hydrogen production efficiency, reduce energy consumption and CO2emission. Sorption complex catalyst is the research priority of ReSER process. In this paper, the main purpose is to improve the activity and stability of the sorption complex catalyst at larger volumetric space velocity in ReSER process by changing preparing methods.A Ni-CaO/Al2O3sorption complex catalyst was prepared by hydrothermal precipitation method in this paper. Layered double hydroxide precursor NiAl-LDHs was obtained by this method in an autoclave, using nickel nitrate, alumina sol, nano-calcium carbonate as materials and urea as precipitation agent. The precursor was calcined to get the Ni-CaO/Al2O3sorption complex catalyst hd-cat. The optimized reaction temperature, urea concentration and calcination temperature were150℃,3mol·L-1and500℃respectively. In addition, another Ni-CaO/Al2O3sorption complex catalyst ci-cat was prepared by impregnation method for comparison.SEM、BET、XRD、XPS、H2-TPD. H2-TPR were carried out to characterize the structure and properties of the sorption complex catalysts. SEM photos showed that catalyst hd-cat had lots of pore channels with porous microscopic structure. BET testing showed that the surface area of hd-cat was134.4m2·g-1and was3.8times that of ci-cat. H2-TPD results showed that the Ni dispersion of hd-cat and ci-cat were9.45%and7.27%respectively.TGA was used to evaluate the CO2adsorption properties of the catalysts. TGA results indicated that the sorption capacity of hd-cat was1.8times that of ci-cat, and the sorption rate of hd-cat was2.7times that of ci-cat. The effect of adsorption temperature on the adsorption properties of hd-cat was also studied. The results showed that the sorption capacity and sorption rate increased during500-650℃with the increase of adsorption temperature, and the adsorption stability was improved.The hydrogen production activity of the two sorption complex catalysts was evaluated in a fixed-bed reactor under temperature of600℃, pressure of0.1MPa, and steam methane molar ratio of4. The results indicate that the maximum space velocity of hd-cat was2376h"’. And under this condition,94.4%of H2concentration and98.4%of CH4conversion were achieved respectively, while under temperature of600℃ci-cat lost its activity at space velocity of1188h-1. When the reaction temperature increasing to650℃, the largest space velocity of hd-cat increases to2970h-1. Then, the stability of hd-cat was studied under reaction temperature of600℃, regeneration temperature of800℃and space velocity of2376h-1. During the10times of reaction-regeneration cycles, both H2concentration and CH4conversion exceeded90%, which revealed that hd-cat had a good stability.The large surface area and high Ni dispersion of catalyst hd-cat are the essential reasons for its good performance in ReSER process. High Ni dispersion ensures lots of reforming reaction activity sites, and large surface area lead to lots of adsorption sites, thus hd-cat can perform well under a large spcace velocity. The microscopic properties before and after ten times of cycles were analysed and compared. The results show that sintering of support, the growth of Ni and embeded of Ni by CaO were the major causes of the deactivation of sorption complex catalyst in ReSER process.