TY - JOUR
T1 - Controlled deposition of silica on titania-silica to alter the active site surroundings on epoxidation catalysts
AU - Alexander Ardagh, M.
AU - Bregante, Daniel T.
AU - Flaherty, David W.
AU - Notestein, Justin M.
N1 - Funding Information:
M.A.A. thanks Louisa Savereide, Scott Nauert, Mihir Bhagat, and Todd Eaton for the helpful discussions and prior syntheses. M.A.A. was supported by the Department of Energy (DOE) through the Institute for Catalysis in Energy Processes (ICEP) and this research was exclusively funded by DOE award # DE-FG02-03-ER154757. D.T.B. and D.W.F. acknowledge support by the U.S. Army Research Office under grant number W911NF-18-1-0100. Metal analysis was performed at the Northwestern University Quantitative Bio-element Imaging Center (QBIC). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by the Argonne National Laboratory under Contract No. DE-AC02-06CH11357. M.A.A. thanks Dr. Qing Ma for his seemingly unlimited patience and assistance with the setup for Ti K-edge XANES.
Publisher Copyright:
© 2020 American Chemical Society
PY - 2020/11/6
Y1 - 2020/11/6
N2 - Lewis acidic Ti-SiO2 materials are workhorse oxidation catalysts, and they range from microporous substituted zeolites to meso/macroporous materials, often with tradeoffs between steric accessibility and activity. In this study, SiO2 is deposited over the active sites of a macroporous, highly dispersed Ti-SiO2 catalyst, with or without an organic template. SiO2 deposition is shown to impact the local environment around epoxidation active sites without altering the active site or introducing diffusion limitations for the representative bulky alkene limonene. Thus, intrinsic activation enthalpies remain nearly constant (45 ± 3 kJ/mol) across all materials and controls, but templated SiO2 deposition gives an apparent activation enthalpy (9 kJ/mol) much lower than that of the other materials tested because of its strong limonene adsorption. This demonstrates independent control of the active site, its immediate surroundings, and the extended pore structure, while also serving the practical purpose of creating a material that can outperform relevant benchmark materials. These types of materials may find utility in the selective transformation of larger reactants, including biorenewables such as limonene, or precursors for pharmaceuticals and other fine chemicals.
AB - Lewis acidic Ti-SiO2 materials are workhorse oxidation catalysts, and they range from microporous substituted zeolites to meso/macroporous materials, often with tradeoffs between steric accessibility and activity. In this study, SiO2 is deposited over the active sites of a macroporous, highly dispersed Ti-SiO2 catalyst, with or without an organic template. SiO2 deposition is shown to impact the local environment around epoxidation active sites without altering the active site or introducing diffusion limitations for the representative bulky alkene limonene. Thus, intrinsic activation enthalpies remain nearly constant (45 ± 3 kJ/mol) across all materials and controls, but templated SiO2 deposition gives an apparent activation enthalpy (9 kJ/mol) much lower than that of the other materials tested because of its strong limonene adsorption. This demonstrates independent control of the active site, its immediate surroundings, and the extended pore structure, while also serving the practical purpose of creating a material that can outperform relevant benchmark materials. These types of materials may find utility in the selective transformation of larger reactants, including biorenewables such as limonene, or precursors for pharmaceuticals and other fine chemicals.
KW - Biorenewables
KW - Kinetics
KW - Limonene
KW - Oxides
KW - Selectivity
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U2 - 10.1021/acscatal.0c02937
DO - 10.1021/acscatal.0c02937
M3 - Article
AN - SCOPUS:85095884826
VL - 10
SP - 13008
EP - 13018
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
IS - 21
ER -