(712b) The Promoting Effect of Mo in NiMo clusters Confined in Zeolite Y and Their Application in Methane Steam Reforming at Low S/C Ratio

Hydrogen has been considered as the future energy carrier because of its environment-friendly and sustainable properties. Currently, nearly 95% of hydrogen is produced from methane steam reforming over nickel-based catalysts which, however, suffer from the deactivation due to severe coke and active sites sintering. To address these issues, we introduce both Ni and Mo precursors into the channel of zeolite Y (Si/Al = 2.6) using an ion-exchange method and solid-phase reaction at elevated temperature, respectively, to form NiMo/Y.26 catalysts. Over NiMo/Y.26 catalyst, the yield of hydrogen was up to 68% at 850 ^oC with S/C ratio of 1.0 and was stable in a 24-hour test period, while the initial hydrogen yield over Ni/Y2.6 was only 36% and decreased to 11% after the 27-hour due to Ni nanoparticle sintering. The influence of S/C ratios on the performance was investigated over Ni/Y2.6 and NiMo/Y2.6. For Ni/Y2.6, its activity was higher at the S/C ratio of 1.5 than at that of 1.0 as predicted. However, the addition of the Mo reversed the activity of NiMo/Y2.6 at the S/C ratio of 1.0 and 1.5. The proposed mechanism for this observation is that the addition of Mo promoter enhances water activation, leading to its high reforming performance even at the extremely low S/C ratio of 1.0, but a S/C ratio of 1.5 leads to the oxidation of Ni active site. Heat pretreatment condition can also influence the performance of NiMo/Y2.6 at S/C ratio of 1.5; calcination at 700 ^oC in the air significantly increases the H₂ yield at the S/C ratio of 1.5 to 70% from 0% which was obtained over NiMo/Y2.6 calcined at 500 ^oC.