TY - JOUR
T1 - Catalytic thiophene oxidation by groups 4 and 5 framework-substituted zeolites with hydrogen peroxide
T2 - Mechanistic and spectroscopic evidence for the effects of metal Lewis acidity and solvent Lewis basicity
AU - Bregante, Daniel T.
AU - Patel, Ami Y.
AU - Johnson, Alayna M.
AU - Flaherty, David W.
N1 - Funding Information:
We thank Ms. Zeynep Ayla for proofreading and editing this manuscript, Ms. Katherine Nagode for technical assistance, and Dr. Damien Guironnet for use of lab equipment to synthesize Ti-BEA. DTB was supported by the Department of Defense (DoD) through the National Defense, Science, and Engineering Graduate (NDSEG) Fellowship Program. This work was carried out, in part, in the Frederick Seitz Materials Research Laboratory Central Research Facilities at the University of Illinois. This work was supported by the U.S. Army Research Office under grant numbers W911NF-16-1-0128 and W911NF-18-1-0100 .
Funding Information:
We thank Ms. Zeynep Ayla for proofreading and editing this manuscript, Ms. Katherine Nagode for technical assistance, and Dr. Damien Guironnet for use of lab equipment to synthesize Ti-BEA. DTB was supported by the Department of Defense (DoD) through the National Defense, Science, and Engineering Graduate (NDSEG) Fellowship Program. This work was carried out, in part, in the Frederick Seitz Materials Research Laboratory Central Research Facilities at the University of Illinois. This work was supported by the U.S. Army Research Office under grant numbers W911NF-16-1-0128 and W911NF-18-1-0100.
Publisher Copyright:
© 2018 Elsevier Inc.
PY - 2018/8
Y1 - 2018/8
N2 - Group 4 (Ti and Zr) and 5 (Nb and Ta) atoms substituted into the *BEA zeolite framework (M-BEA) irreversibly activate hydrogen peroxide (H2O2) and form pools of metal-hydroperoxide (M-OOH) and peroxide (M-(η2-O2)) intermediates active for the oxidation of 2,5-dimethylthiophene (C6H8S), a model reactant representative of organosulfur species in fossil reserves and chemical weapons. Sequential oxidation pathways convert C6H8S into 2,5-dimethylthiophene oxide (C6H8SO) and subsequently into 2,5-dimethylthiophene dioxide by oxidative dearomatization. Oxidation rates measured as functions of reactant concentrations together with in situ UV–vis spectra show that all M-BEA activate H2O2 to form pools of M-OOH and M-(η2-O2), which then react with either C6H8S or H2O2 to form the sulfoxide or to decompose into H2O and O2, respectively. Turnover rates for C6H8S oxidation and H2O2 decomposition both increase exponentially with the electron affinity of the active site, which is quantitatively probed via the adsorption enthalpy for deuterated acetonitrile to active sites. C6H8S oxidation rates depend also on the nucleophilicity of the solvent used, and rates decrease in the order acetonitrile > p-dioxane ∼ acetone > ethanol ∼ methanol. In situ UV–vis spectra show that highly nucleophilic solvent molecules compete effectively for active sites, inhibit H2O2 activation and formation of reactive M-OOH and M-(η2-O2) species, and give lower turnover rates. Consequently, this work shows that turnover rates for sulfoxidation are highest when highly electrophilic active sites (i.e., stronger Lewis acids) are paired with weakly nucleophilic solvents, which can guide the design of increasingly productive catalytic systems for sulfide oxidation.
AB - Group 4 (Ti and Zr) and 5 (Nb and Ta) atoms substituted into the *BEA zeolite framework (M-BEA) irreversibly activate hydrogen peroxide (H2O2) and form pools of metal-hydroperoxide (M-OOH) and peroxide (M-(η2-O2)) intermediates active for the oxidation of 2,5-dimethylthiophene (C6H8S), a model reactant representative of organosulfur species in fossil reserves and chemical weapons. Sequential oxidation pathways convert C6H8S into 2,5-dimethylthiophene oxide (C6H8SO) and subsequently into 2,5-dimethylthiophene dioxide by oxidative dearomatization. Oxidation rates measured as functions of reactant concentrations together with in situ UV–vis spectra show that all M-BEA activate H2O2 to form pools of M-OOH and M-(η2-O2), which then react with either C6H8S or H2O2 to form the sulfoxide or to decompose into H2O and O2, respectively. Turnover rates for C6H8S oxidation and H2O2 decomposition both increase exponentially with the electron affinity of the active site, which is quantitatively probed via the adsorption enthalpy for deuterated acetonitrile to active sites. C6H8S oxidation rates depend also on the nucleophilicity of the solvent used, and rates decrease in the order acetonitrile > p-dioxane ∼ acetone > ethanol ∼ methanol. In situ UV–vis spectra show that highly nucleophilic solvent molecules compete effectively for active sites, inhibit H2O2 activation and formation of reactive M-OOH and M-(η2-O2) species, and give lower turnover rates. Consequently, this work shows that turnover rates for sulfoxidation are highest when highly electrophilic active sites (i.e., stronger Lewis acids) are paired with weakly nucleophilic solvents, which can guide the design of increasingly productive catalytic systems for sulfide oxidation.
KW - Competitive adsorption
KW - Lewis acid catalysis
KW - Mayr nucleophilicity
KW - Oxidative desulfurization
KW - Solvent effects
KW - Zeolite catalysis
UR - http://www.scopus.com/inward/record.url?scp=85048937343&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85048937343&partnerID=8YFLogxK
U2 - 10.1016/j.jcat.2018.06.009
DO - 10.1016/j.jcat.2018.06.009
M3 - Article
AN - SCOPUS:85048937343
VL - 364
SP - 415
EP - 425
JO - Journal of Catalysis
JF - Journal of Catalysis
SN - 0021-9517
ER -