Reverse water-gas shift reaction on MoOx/β-, Y-, ZSM-5 commercial zeolites: Effect of acid/base properties

Herein, the influence of different zeolite topologies and acid-base properties of commercial HZSM-5 (MFI, 10-membered ring), beta-(BEA, 12-membered ring), and Y-zeolites (FAU, 12-membered ring) on MoO x species formation and its resultant effect on reverse water-gas shift (rWGS) reaction in the mid-temperature range of 350-450°C under atmospheric pressure was investigated. Principally, MoO x clusters in 10 wt.% Mo/zeolite catalysts were distributed on the surface of the zeolites with a minor portion in micropores. Ease of reduction of MoO 3 into MoO 2 was observed in 10Mo/ZSM-5, followed by 10Mo/beta- and 10Mo/Y-zeolite catalysts as established through temperature programmed reduction (H 2 -TPR) and X-ray diffraction (XRD) results. Further, greater acid/base properties and superior hydrogen holding tendency of MoO 2 in 10Mo/ZSM-5 observed through temperature programmed desorption (TPD; NH 3 -TPD, CO 2 -TPD, and H 2 -TPD) data resulted in greater CO 2 conversion (30.0-41.0%) and methane formation. Whereas, 10Mo/Y-zeolite catalysts showed the lowest CO 2 conversions (25.0-37.0%) with reasonably good CO selectivity (93.0-96.0%) at 450°C. It was likely due to the weak sorption strength for CO 2 /H 2(g) molecules with prominent MoO 3 clusters that existed on Y-zeolite demonstrated via TPD, XRD, and Raman data. However, on the other hand, 10Mo/beta-zeolite catalysts emerged with moderate acid-base properties, with MoO 2 /MoO 3 mixed phases eventually resulting in reasonable CO 2 conversions (27.0-40.0%) with superior CO selectivity (95.0-99.0%). Thus, zeolite topology and acid-base properties influenced the rWGS reaction performance in 10MoOx/zeolite (commercial) catalysts and are beneficial for further studies.