Chemical and Materials Sciences: Research Findings Vol. 8

CO₂-assisted propane dehydrogenation offers a route to propylene production in which carbon dioxide can influence reaction equilibrium, hydrogen removal, and catalyst carbonisation. This chapter compares post-synthetically modified M-BEA zeolite catalysts containing Ga(Ta, Nb), Cr/Zn, and Zn(Y), with emphasis on relationships among metal identity, surface acid–base properties, activity, selectivity, and stability. The catalysts were prepared by dealumination of BEA zeolite followed by incorporation of the relevant metal cations and were characterised using XRD, XPS, NMR, nitrogen adsorption/desorption, temperature-programmed desorption and oxidation, hydrogen temperature-programmed reduction, and FTIR spectroscopy of adsorbed pyridine. Catalytic performance was evaluated at 500–650 °C, including time-on-stream tests of 2.5 and 10 h. Regeneration behaviour was also examined after carbon removal in an oxidising gas mixture. The findings indicate that balanced acid–base characteristics govern performance. Medium-strength Lewis acid sites support propane activation, whereas strong Brønsted acid sites promote cracking and oligomerisation, leading to carbon deposition and loss of accessible surface area. Basic sites influence CO₂ conversion and can contribute to limiting carbon accumulation. Among the systems examined, Ga₄.₀SiBEA and Zn₂.₀SiBEA achieved high propylene yields, while Zn₂.₀SiBEA showed greater stability during prolonged operation. The BEA framework remained structurally stable, and regeneration substantially restored catalytic performance. Overall, catalyst stability depended primarily on controlling surface acidity and carbon formation.