Ethanol Conversion to Linear Olefin Over Phosphorus-Modified Beta Zeolite Catalysts

This study experimentally investigates the effects of modification techniques (post-synthesis impregnation and isomorphous substitution), phosphorus loading, Si/Al ratio, and time on stream on the performance of zeolite-based catalysts in the selective conversion of ethanol into linear olefins. Firstly, the involved catalysts (i.e., pristine and phosphorus-modified beta zeolites) have been characterized using Nuclear magnetic resonance (NMR), temperature-programmed desorption of ammonia (NH₃-TPD), X-ray diffraction (XRD), thermogravimetric analysis (TGA), N₂ physisorption, ³¹P MAS NMR, and Energy-dispersive X-ray spectroscopy (STEM-EDS). These characterization tests are employed to monitor the impact of phosphorus loading on the structural, textural, acidic, and hydrophobic properties of the zeolite-based catalysts. Increasing the modifying the phosphorus loading of the beta zeolite from 0 to 5 wt% increases ethanol conversion from 92 to 94% and improves their selectivity toward C₄-C₁₂ linear olefins from 52 to 72%. Also, modifying the beta zeolite by the post-synthesis impregnation method results in higher ethanol conversion and lower selectivity toward linear olefins than the isomorphous substitution approach. Increasing the Si/Al ratio from 25 to 50 results in decreasing the ethanol conversion from 94 to 85% and increasing the selectivity towards C₄-C₁₂ linear olefins from 63 to 70% for the catalyst containing 3 wt% of phosphorus. Experimental data is employed to propose a reaction mechanism and elucidate the fundamental roles of phosphorus loading in regulating the reaction pathways. The findings of this study provide valuable insights into the design and optimization of phosphorus-modified zeolite catalysts, enabling the efficient and selective production of linear olefins from ethanol.