| Reactive sorption enhanced reforming (ReSER) is a new method for hydrogen production with energy saving and CO2 emission reduction. The equilibrium of steam methane reforming reaction has been broken through by using adsorption to remove the CO2. It can reduce the reaction temperature and the energy consumption, so it is significant for the chemical industry, the refinery industry and future energy economy. Researches found that sorption complex catalyst's activity declined after several reaction cycles in ReSER process is a primary issue to be resolved in commercial applications.This research concerned on a preparation method of the Ni-nano CaO sorption complex catalyst. The influences of preparation conditions such as calcination temperature and ZrO2 content on complex catalyst's performance were studied. Catalyst's activity and stability in ReSER were evaluated on a laboratory scale fixed-bed reactor.Carbon deposition content of catalysts were detected by thermo-gravity analyzer (TGA).Catalyst morphology and the particle sizes were characterized by transmission electron microscope(TEM), while reduction temperature of metal oxide were characterized by temperature programmed reduction(TPR). The influences of modification with ZrO2 on these properties were observed. The results indicated the complex catalysts carbon deposition ratio were less than 1%; the particle size of ZrO2 was 4-10nm, which was dispersed on surface of nano-CaCO3; ZrO2-modified has a decrease of reduction temperature of NiO from 430℃to 280℃.The performance of ZrO2-modified complex catalyst was evaluated on a laboratory scale fixed-bed reactor. In the optimization condition, of which reaction temperature is 600℃, reaction pressure 0.1 MPa and the water to carbon mole ratio 4, 97.3% percent H2(on dry basis) was produced and the corresponding CH4 conversion was 93.7%. ZrO2-modified complex catalyst deactivated after 20 ReSER cycles, whereas non-ZrO2-modified complex catalyst deactivated only after 5 ReSER cycles. ZrO2-modified complex catalyst clearly exhibited better stability compared to non-ZrO2-modified complex catalyst.The crystal structures of the catalyst were determined by X-ray diffraction (XRD). The BET surface area and the distribution of pore volume were measured by nitrogen adsorption. Results indicated that modification with ZrO2 can significantly increase the catalyst surface area (from 30.9m2/g to 69.5m2/g). Further researches showed catalyst surface area had no direct relation with ZrO2 content. The research on calcination temperature showed that, with the increase of calcination temperature, the surface area of complex catalysts decreased. The temperature range of 500-600℃was selected as the optimal reforming reaction temperature. XRD results showed that the crystal size of NiO increased from 17.68nm to 32.95nm,12.12nm to19.32nm respectively。The reasons for ZrO2 increased the catalytic activity and stability were analyzed. TPR results showed that the interaction between NiO and ZrO2 was stronger than that of NiO and Al2O3. It prohibited the formation of NiAl2O4 High oxygen storage capacity of ZrO2 made the catalyst provide plenty of lattice oxygen (Ox) in ReSER, which can prevent the formation of carbon species. The results had an important significance on the guidance of the improving for catalysts in ReSER. |
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