Probing deactivation by coking in catalyst pellets for dry reforming of methane using a pore network model

Dry reforming of methane(DRM) is an attractive technology for utilizing the greenhouse gases(CO_(2) and CH_(4)) to produce syngas. However, the catalyst pellets for DRM are heavily plagued by deactivation by coking, which prevents this technology from commercialization. In this work, a pore network model is developed to probe the catalyst deactivation by coking in a Ni/Al_(2)O_(3) catalyst pellet for DRM. The reaction conditions can significantly change the coking rate and then affect the catalyst deactivation. The catalyst lifetime is higher under lower temperature, pressure, and CH_(4)/CO_(2) molar ratio, but the maximum coke content in a catalyst pellet is independent of these reaction conditions. The catalyst pellet with larger pore diameter, narrower pore size distribution and higher pore connectivity is more robust against catalyst deactivation by coking, as the pores in this pellet are more difficult to be plugged or inaccessible.The maximum coke content is also higher for narrower pore size distribution and higher pore connectivity, as the number of inaccessible pores is lower. Besides, the catalyst pellet radius only slightly affects the coke content, although the diffusion limitation increases with the pellet radius. These results should serve to guide the rational design of robust DRM catalyst pellets against deactivation by coking.

Catalytic behavior in propane aromatization using GA-MFI catalyst

Ga-Al-MFI samples were synthesized in hydrothermal conditions from gels of composition 1.08CH3NH2- 0.134TPABr-1SiO2-xAl2O3-yGa2O3-40H2O at 175 ℃ for 7 days, with x = 0.005 and 0.0025, y = 0.005, 0,010 and 0.020. The samples were characterized by XRD, BET measurements, thermal analysis （TGA-DTA） atomic absorption and high resolution solid state MAS 27Al and 71Ga NMR measurements. The aromatization of propane was studied as catalytic test. The activity and selectivity of the catalysts were determined for benzene, toluene and xylenes on the one hand and for methane and ethane on the other hand. The most active sample was obtained with the highest Ga/AI ratio. For this sample, the BTX selectivity obtained by aromatization was always higher than the hydrocracking selectivity leading to methane and ethane. The relative amount of toluene was higher than that of benzene and ofxylenes. The samples were deactivated by coke formation that was revealed more severe for the most active sample,