Generation of acid catalytic activity in Si-VPI-5 by partial Si for P substitution during hydrothermal synthesis

Transition-metal-free microporous and mesoporous catalysts for the epoxidation of cyclooctene with hydrogen peroxide

“…The formation of the desired AFI structure was confirmed by powder XRD analysis. VPI-5 (VFI) was prepared as described previously [21]. First, 10.92 g of pseudoboehmite was mixed with 32.40 g of bi-distilled water.…”

Tailored Catalytic Propene Trimerization over Acidic Zeolites with Tubular Pores

“…Zeolite samples were synthesized according to published methods: ZSM-22, [26] ZSM-23 was run 4 of reference [27], ZSM-48, [28] SAPO-11 [29] was sample S-11/2 of reference [30]. The Si/Al ratio of ZSM-22, -23, and -48 was 42, 44, and 50, respectively.…”

“…The SAPO-11 crystals are composed of 28 % aluminosilicate (AS) and 72 % silicoaluminophosphate (SAP) domains. [30] The catalytic activity of SAPO-11 is mainly due to Brønsted acid sites at the interphase between the AS and SAP domains.…”

Gas-phase dehydration of glycerol over thermally-stable SAPO-40 catalyst

“…However, depending on the initial amount of silicon in the synthesis gel and other experimental parameters, the incorporation may also occur by mechanism SM3, where two Si atoms substitute a pair of neighbouring P and Al leading to the formation of silicon islands. Due to different silicon environments, the acid sites located at the edges of silicon islands were proved to have higher strength than those resulting from isolated Si atoms [29][30][31][32] . Therefore, the silicon distribution in the various SAPO-samples is an important feature that plays a key role in the catalytic activity.…”

“…This is particularly evident in the case of SAPO-11 where the number of Lewis acid sites is higher than the number of Brönsted sites (table 1), but the selectivity obtained clearly suggests the predominance of Brönsted sites. Although the acidity of SAPO-34 cannot be assessed using pyridine 35 , from the silicon distribution evidenced by 29 Si NMR it is expected that SAPO-34, with a low amount of silica domains, should comprise mainly weak Brönsted acid sites where the presence of silica domains in the other materials may give rise to Brönsted acid sites with higher strenght 22,[29][30][31][32] .…”