Influence of metal doping on the coke formation of a novel hierarchical HZSM-5 zeolite catalyst in the conversion of 1-propanol to fuel blendstock

Abstract

In this work, the effect of Ni doping on coke formation and the activity of a novel hierarchical HZSM-5 zeolite catalyst in the conversion of 1-propanol to fuel blends was investigated. The catalysts, which were hydrothermally synthesised and modified with 0.5 wt% Ni, were characterised using different techniques (XRD, FTIR, SEM, PSD, N₂ adsorption, NH₃-TPD, TGA-DTA) and tested at 350–400 °C and, WHSV of 7 and 12 h⁻¹ for the conversion of 1-propanol into fuel blendstocks. The catalyst characterisation results confirmed the successful synthesis of hierarchical HZSM-5 and the incorporation of nickel. The catalytic results showed that both catalysts exhibited >98% 1-propanol conversion with considerable selectivity (>80%) for jet fuel and (>50%) gasoline blendstock. While Ni/HZSM-5 favoured jet fuel, the undoped catalyst improved gasoline production. The stability and deactivation study showed that HZSM-5 exhibited greater long-term stability and maintained a conversion rate of >95%, making it well-suited for the extended conversion of 1-propanol. The moderate production of jet fuel and the uniform selectivity of gasoline indicate a balanced distribution of products. In contrast, Ni/HZSM-5 initially provides higher jet fuel production and stable gasoline production, but the conversion rate drops more sharply after 40 h on stream, which is due to rapid deactivation by coke accumulation or deactivation of metal sites. The coking study showed that the Ni-doped catalysts produced more coke, resulting in a weight loss of 6.4 wt% compared to the unmodified catalysts (6.1 wt%), which contributed to their deactivation, as evidenced by a reduction in 1-propanol conversion. Characteristic spectral bands from the analysis of the spent catalysts indicated the composition of the coke present, with key regions at 1300–1700 cm⁻¹ and 2800–3100 cm⁻¹ showing that the spent catalysts consisted of polycondensed aromatics, conjugated olefins and aliphatics. It can be concluded that the metal modification improves the catalytic performance but increases the coking and deactivation tendencies compared to the unmodified catalyst, which may limit the stability of the catalyst.