IM-5 zeolite with abundant narrow mesopores and modulated acidity as stable and selective cracking catalyst

Abstract

High-performance IM-5 was prepared by tetrapropylammonium hydroxide (TPAOH) and NaOH alkaline treatment. The modification of combined alkaline treatment on the pore and acidity were systematically characterized. The 29 Si NMR results indicated that Si(4Si, 0Al) sites were protected by tetrapropylammonium cation (TPA + ) at low TPAOH/(NaOH + TPAOH) molar ratio, while the protection effect extended to some Si(3Si, 1Al) sites at TPAOH/(NaOH + TPAOH) ratio of 75%. And, the amount of strong Brønsted acid sites decreased significantly from 255 μmolg −1 to 119 μmolg −1 under the optimal TPAOH/NaOH alkaline treatment conditions. Compared to NaOH treatment alone, the mesopore volume and external surface area of IM-5 were further increased with TPAOH introduced, meanwhile, the mesopore size was shrunken into the range of 2–10 nm centered at 5 nm. Compared to NaOH treated IM-5 catalyst, the TPAOH/NaOH treated one exhibited higher initial light olefins yield (53.4% vs. 45.2% for n -heptane cracking) and better catalytic stability and regeneration properties. The abundant narrow mesopores contributed into high tolerance ability to coke deposition in IM-5 catalysts, as confirmed by TGA results. • TPAOH/NaOH treatment led to abundant well-spread mesopores in IM-5. • TPAOH/NaOH treatment lowered the amount of strong Brønsted acid sites. • TPA + extended protection effect to framework aluminum at high TPAOH concentration. • TPAOH/NaOH treated IM-5 reached high light olefins yield of 53.4%. • TPAOH/NaOH treated IM-5 kept stable in 5 regeneration cycles.