Effect of Si/Al ratio of mordenite and ZSM5 type zeolite catalysts on hydrothermal stability for NO reduction by hydrocarbons

Selective Transformation of Various Nitrogen-Containing Exhaust Gases toward N2 over Zeolite Catalysts

“…Hydrothermal stability plays a decisive role in practical applications of zeolite catalysts, especially for the SCR of NO with NH 3 and the selective catalytic oxidation (SCO) of NH 3 and nitriles, wherein the presence of water vapor in the effluent gases might cause the framework to collapse due to unavoidable dealumination at high temperatures. − Chung et al investigated the effect of the Si/Al ratio on the hydrothermal stability of MOR and MFI catalysts for NO reduction by hydrocarbons. It was observed that the Si/Al ratio was the most critical characteristic determining the hydrothermal stability of the zeolite catalysts.…”

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

“…60,151,200,222 Thus, better molybdenum anchoring to the zeolite framework obtained with low Si/Al ratios offsets the weaker (hydro)thermal stability of aluminum-rich zeolites. 246,247 As an alternative way, the preparation of atomically dispersed Mo/ HZSM-5 catalysts by defect "healing" of the framework structure with molybdenum was reported. 186,248−250 The Mo was introduced in the silanol nest defects of the MFI zeolite framework resulting in ultrastable catalysts.…”

“…The robustness of impregnated Mo/HZSM-5 catalyst is inherent in the zeolite framework in the presence of alumina. To mitigate the irreversible deactivation of the catalyst, Mo-support interactions, i.e., the balance between Mo and Si/Al ratio of the zeolite is a critical parameter to be considered. ,,, High molybdenum content favors its migration phenomena, and the optimal molybdenum content for the HZSM-5 catalyst with a Si/Al ratio of 15 was found to be around 4–5 wt %. ,,, Thus, better molybdenum anchoring to the zeolite framework obtained with low Si/Al ratios offsets the weaker (hydro)­thermal stability of aluminum-rich zeolites. , As an alternative way, the preparation of atomically dispersed Mo/HZSM-5 catalysts by defect “healing” of the framework structure with molybdenum was reported. ,− The Mo was introduced in the silanol nest defects of the MFI zeolite framework resulting in ultrastable catalysts. The atomically dispersed Mo/HZSM-5 depicted high stability of both the zeolite structure and the molybdenum during multiple cycles of MDA reaction at 850 °C and regeneration at 750 °C under steaming.…”