Mass-Transfer Enhancement in the CO2 Oxidative Dehydrogenation of Propane over GaN Supported on Zeolite Nanosheets with a Short b-Axis and Hierarchical Pores

Abstract

The CO₂ oxidative dehydrogenation of propane (CO₂–ODHP) is a highly important reaction for not only producing large amounts of propylene but also consuming the CO₂ resource. GaN/zeolite catalysts deliver preferable activity in the reaction. However, similar to Pt- and Cr-based catalysts, there are shortcomings such as poor stability and coke accumulation, especially when operated at temperatures higher than 550 °C. Generally, carbon deposition is one of the main reasons for catalyst deactivation. The limited mass transfer greatly aggravates the deposited carbon formation, since carbon precursors could not be removed in time. In the present work, we modified zeolites with a short b-axis and hierarchical pores, which could offer a shorter diffusion distance and pore-rich structure to enhance the mass transfer. Thanks to this enhancement, the catalyst offers an initial propane conversion of 68.0% with a yield of 39.4% to propylene, surpassing other reported GaN/zeolite catalysts to data. Importantly, the catalyst showed a low loss rate of activity and a low amount of deposited carbon, which was easily regenerated compared with those of other catalysts without a short b-axis or hierarchical pores. Density functional theory (DFT) calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed that the reaction involves a coupling reaction of direct dehydrogenation and CO₂ reduction via reverse water–gas shift reaction, and CO₂ participates in the reaction. The present work sheds light on designing an efficient catalyst for CO₂–ODHP via a mass transfer-boosted strategy and, importantly, is expected to provide inspiration in constructing a zeolite with a short b-axis and hierarchical pores.