Can Metal Promotion of SAPO-34 Genuinely Improve Its Catalytic Performance in Methanol Conversion to Light Olefins Reaction?

To genuinely assess the effect of secondary metal promotion on improving the SAPO-34 catalytic performance in MTO reaction, a broad spectrum of metals from different groups of the periodic table (alkali and alkaline earth metals, transition metals, rare earth metals, and basic metals) were investigated. Metals were added through a direct incorporation route with Me/Al2O3 molar ratio of 0.05. Some metals seamlessly incorporated into the SAPO-34 framework and replaced the Si and Al atoms, while others partially merged or even failed to be combined with SAPO and emerged as amorphous phases. Although, in some cases, the surface area of the metal-promoted samples increased due to enhanced nucleation rate and smaller particle formation, the majority of the promoted samples suffered from a severe loss in crystallinity that resulted in inferior catalytic performance. It was also illustrated that hydrogen co-feeding with methanol (H2/MeOH molar ratio of 1.5) at ambient pressure could extend the catalyst lifetime by 27 % due to hydrogenation and cracking of the coke species and improve the light olefins selectivity.