Dry Reforming of Methane over Ni-Cu/Al2O3 Catalyst Coatings in a Microchannel Reactor: Modeling and Optimization Using Design of Experiments

In the present research, synthesis gas was produced through dry reforming of methane (DRM) in a microchannel reactor. First, a layer of Al2O3 was sputtered and deposited on a stainless steel plate, to prepare metallic catalyst support; then, a layer of Ni-Cu catalyst was deposited on the Al2O3. After undergoing a high-temperature DRM reaction, the catalyst-coated plates were tested and the fall-off rate was negligible because a firm active catalyst coating was formed. Using response surface methodology (RSM), deposition time (1, 3, and 5 min), Cu/Ni surface area percentage (10, 20, and 30%), and reaction temperature (700, 750, and 800 degrees C) were selected as the operating variables to investigate and optimize initial feed conversion, catalyst deactivation, and H-2:CO ratio. Grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) techniques were used to characterize Ni-Cu/Al2O3 catalyst coatings. Based on the results of GIXRD analysis, with increasing Cu/Ni surface area percentage up to 20%, there was a reduction in the particle size; however, when Cu/Ni surface area percentage increased further, the particle size increased. Moreover, in plates undergoing a longer time of deposition, the FESEM images showed denser grains that well-covered the substrate. EDX analysis indicated a proper dispersion, and the results confirmed the presence of the utilized elements. Overall, the results proved the significant impact of Cu percentage on the performance of the catalyst. The catalyst activity and stability during the reaction were higher in a promoted catalyst with low amounts of Cu, compared to the catalyst coated with high amounts of Cu. Under optimum conditions, i.e., the deposition time of 3.85 min, reaction temperature of 800.00 degrees C, and Cu/Ni surface area percentage of 18.39%, the initial conversions of CH4 and CO2 were 95.9975 and 98.7682%, respectively; the rate of deactivation of the catalyst was 0.493989%; and the H-2:CO ratio was 0.969994. There was a good level of consistency between values obtained from the analysis of variance model and the results of the experimental tests. Furthermore, under the optimum conditions, the catalyst was not deactivated for 30 h on stream. Hence, the use of Ni-Cu/Al2O3 thin film in the designed microchannel showed satisfactory performance. Based on our findings, the designed reactor has a good performance, is compact enough, and is cost-effective. Thus, the technique utilized in this study is a convenient and favorable method for preparing high-performance structured catalysts.