Post-Synthesis Strategies to Prepare Mesostructured and Hierarchical Silicates for Liquid Phase Catalytic Epoxidation

Abstract

Olefin epoxidation is an important transformation for the chemical valorization of olefins, which may derive from renewable sources or domestic/industrial waste. Different post-synthesis strategies were employed to introduce molybdenum species into mesostructured and hierarchical micro-mesoporous catalysts of the type TUD-1 and BEA, respectively, to confer epoxidation activity for the conversion of relatively bulky olefins (e.g., biobased methyl oleate, DL-limonene) to epoxide products, using tert-butyl hydroperoxide as an oxidant. The influences of (i) the type of metal precursor, (ii) type of post-synthesis impregnation method, (iii) type of support and (iv) top-down versus bottom-up synthesis methodologies were studied to achieve superior catalytic performances. Higher epoxidation activity was achieved for a material prepared via (post-synthesis) incipient wetness impregnation of MoO2(acac)2 (acac = acetylacetonate) on (pre-treated) siliceous TUD-1 and calcination; for example, methyl oleate was converted to the corresponding epoxide with 100% selectivity at 89% conversion (70 °C). Catalytic and solid-state characterization studies were conducted to shed light on material stability phenomena.

Chemical valorisation of biomass derived furanics and carboxylic acids over niobium-based catalysts

“…Pristine silica TUD-1 was prepared in a similar fashion, but without the Nb 2 O 5 nanoparticles, as described in the literature. 71…”

“…The textural properties were somewhat comparable to those of the mesoporous silica TUD-1 (synthesized in a similar fashion, but without Nb 2 O 5 ) which possessed S BET = 471 m 2 g −1 and d p = 8.5 nm. 71…”

“…Pristine silica TUD-1 was prepared in a similar fashion, but without the Nb 2 O 5 nanoparticles, as described in the literature. 71 ambient temperature. The sample was prepared in a spinning flat plate sample holder and step-scanned in the 2θ range from 3°to 70°with steps of 0.026°.…”

“…The textural properties were somewhat comparable to those of the mesoporous silica TUD-1 (synthesized in a similar fashion, but without Nb 2 O 5 ) which possessed S BET = 471 m 2 g −1 and d p = 8.5 nm. 71 The SiNbx materials consisted of niobium oxide nanoparticles (ca. 5 nm) uniformly distributed within mesoporous silica, with Nb at.% relative to Si of 7, 20, 42, 65 and 82; the specific surface area (S BET ) of the SiNbx was in the range 224-913 m 2 g −1 and the average mesopore sizes were in the range 7-27 nm (Table S4 †).…”

Bulky olefin epoxidation under mild conditions over Mo-based oxide catalysts

“…A literature survey for Mo-containing silica/silicates tested in the epoxidation of MeOle or MeLin, indicated two previous studies. 104,105 Gao et al 105 reported the epoxidation of MeOle with H 2 O 2 , in the presence of molybdenum supported on the external surface of TS-1, which led to ca. 65% MeOleEp selectivity at ca.…”