TY - JOUR
T1 - Identifying the roles of acid-base sites in formation pathways of tolualdehydes from acetaldehyde over MgO-based catalysts
AU - Lusardi, Marcella
AU - Struble, Thomas
AU - Teixeira, Andrew R.
AU - Jensen, Klavs F.
N1 - Funding Information:
This work was funded by BP through the MIT Energy Initiative Advanced Conversion Research Program. The authors gratefully acknowledge Professor Yuriy Román and his group members for sharing instrumentation that allowed us to run the N2 adsorption–desorption and DRIFTS experiments. The authors thank Lagnajit Pattanaik and Professor Bill Green for performing the DFT calculations on their machines, and Professor Haomiao Zhang for his help with ASPEN calculations. The authors also greatly appreciate the insight of collaborators at BP, in particular Casey Hetrick, John Shabaker, and Eric Doskocil.
Publisher Copyright:
© The Royal Society of Chemistry 2020.
PY - 2020
Y1 - 2020
N2 - Pure and Al-substituted MgO catalysts are studied to identify the contributions of acid-base sites in the formation of two valuable xylene analogs, ortho- and para-tolualdehydes, from an ethanol derivative, acetaldehyde. The catalyst properties are characterized through XRD, 27Al MAS NMR, ICP-AES, N2 physisorption, TPD-MS, and DRIFTS experiments. Reactivity comparisons of untreated and CO2-titrated catalysts at 250 °C, coupled with CO2 DRIFTS studies on fresh and spent samples, indicate the formation of tolualdehydes from intermediates is initiated through deprotonation by a medium-strength basic site in a specific, metal-oxygen (M-O)-type coordination environment. Analyses of the catalytic surface properties and reactivity, pathways of formation, and natural bond orbital (NBO) charge distribution suggest C4 + C4 (rather than C2 + C6) mechanistic steps dominate tolualdehyde production over these catalysts under the investigated reaction conditions. Isomeric selectivity to ortho-tolualdehyde is 92 and 81 mol% over pure and Al-substituted MgO catalysts, respectively. We propose that the shift in isomeric selectivity towards para- upon introduction of a proximal Lewis acidic functionality (Al3+/MgO) to the catalyst is caused by electron redistribution in the conjugated enolate from the γ-C (forming ortho-) towards the α-C (forming para-) due to the carbonyl-O/Lewis acid coordination. This insight provides a framework for the development of next generation catalysts that give improved reactivity in cascade reactions of C2 feedstocks to aromatics.
AB - Pure and Al-substituted MgO catalysts are studied to identify the contributions of acid-base sites in the formation of two valuable xylene analogs, ortho- and para-tolualdehydes, from an ethanol derivative, acetaldehyde. The catalyst properties are characterized through XRD, 27Al MAS NMR, ICP-AES, N2 physisorption, TPD-MS, and DRIFTS experiments. Reactivity comparisons of untreated and CO2-titrated catalysts at 250 °C, coupled with CO2 DRIFTS studies on fresh and spent samples, indicate the formation of tolualdehydes from intermediates is initiated through deprotonation by a medium-strength basic site in a specific, metal-oxygen (M-O)-type coordination environment. Analyses of the catalytic surface properties and reactivity, pathways of formation, and natural bond orbital (NBO) charge distribution suggest C4 + C4 (rather than C2 + C6) mechanistic steps dominate tolualdehyde production over these catalysts under the investigated reaction conditions. Isomeric selectivity to ortho-tolualdehyde is 92 and 81 mol% over pure and Al-substituted MgO catalysts, respectively. We propose that the shift in isomeric selectivity towards para- upon introduction of a proximal Lewis acidic functionality (Al3+/MgO) to the catalyst is caused by electron redistribution in the conjugated enolate from the γ-C (forming ortho-) towards the α-C (forming para-) due to the carbonyl-O/Lewis acid coordination. This insight provides a framework for the development of next generation catalysts that give improved reactivity in cascade reactions of C2 feedstocks to aromatics.
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U2 - 10.1039/c9cy01927h
DO - 10.1039/c9cy01927h
M3 - Article
AN - SCOPUS:85078694347
SN - 2044-4753
VL - 10
SP - 536
EP - 548
JO - Catalysis Science and Technology
JF - Catalysis Science and Technology
IS - 2
ER -