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Title: Methanol Synthesis from CO2 Hydrogenation over a Pd4/In2O3 Model Catalyst: A Combined DFT and Kinetic Study

Abstract

Methanol synthesis from CO2 hydrogenation on Pd4/In2O3 has been investigated using density functional theory (DFT) and microkinetic modeling. In this study, three possible routes in the reaction network of CO2 + H2 → CH3OH + H2O have been examined. Our DFT results show that the HCOO route competes with the RWGS route whereas a high activation barrier kinetically blocks the HCOOH route. DFT results also suggest that H2COO* + H* ↔ H2CO* +OH* and cis-COOH* + H* ↔CO* + H2O* are the rate limiting steps in the HCOO route and the RWGS route, respectively. Microkinetic modeling results demonstrate that the HCOO route is the dominant reaction route for methanol synthesis from CO2 hydrogenation. We found that the activation of H adatom on the small Pd cluster and the presence of H2O on the In2O3 substrate play important roles in promoting the methanol synthesis. The hydroxyl adsorbed at the interface of Pd4/In2O3 induces the transformation of the supported Pd4 cluster from a butterfly structure into a tetrahedron structure. This important structure change not only indicates the dynamical nature of the supported nanoparticle catalyst structure during the reaction but also shifts the final hydrogenation step from H2COH to CH3O.

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1155126
Report Number(s):
PNNL-SA-98805
39947; KC0302010
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Catalysis, 317:44-53
Country of Publication:
United States
Language:
English
Subject:
CARBON DIOXIDE; INDIUM OXIDES; PALLADIUM; methanol synthesis; carbon dioxide; indium oxide; palladium; density functional theory; kinetic modeling; Environmental Molecular Sciences Laboratory

Citation Formats

Ye, Jingyun, Liu, Changjun, Mei, Donghai, and Ge, Qingfeng. Methanol Synthesis from CO2 Hydrogenation over a Pd4/In2O3 Model Catalyst: A Combined DFT and Kinetic Study. United States: N. p., 2014. Web. doi:10.1016/j.jcat.2014.06.002.
Ye, Jingyun, Liu, Changjun, Mei, Donghai, & Ge, Qingfeng. Methanol Synthesis from CO2 Hydrogenation over a Pd4/In2O3 Model Catalyst: A Combined DFT and Kinetic Study. United States. doi:10.1016/j.jcat.2014.06.002.
Ye, Jingyun, Liu, Changjun, Mei, Donghai, and Ge, Qingfeng. Fri . "Methanol Synthesis from CO2 Hydrogenation over a Pd4/In2O3 Model Catalyst: A Combined DFT and Kinetic Study". United States. doi:10.1016/j.jcat.2014.06.002.
@article{osti_1155126,
title = {Methanol Synthesis from CO2 Hydrogenation over a Pd4/In2O3 Model Catalyst: A Combined DFT and Kinetic Study},
author = {Ye, Jingyun and Liu, Changjun and Mei, Donghai and Ge, Qingfeng},
abstractNote = {Methanol synthesis from CO2 hydrogenation on Pd4/In2O3 has been investigated using density functional theory (DFT) and microkinetic modeling. In this study, three possible routes in the reaction network of CO2 + H2 → CH3OH + H2O have been examined. Our DFT results show that the HCOO route competes with the RWGS route whereas a high activation barrier kinetically blocks the HCOOH route. DFT results also suggest that H2COO* + H* ↔ H2CO* +OH* and cis-COOH* + H* ↔CO* + H2O* are the rate limiting steps in the HCOO route and the RWGS route, respectively. Microkinetic modeling results demonstrate that the HCOO route is the dominant reaction route for methanol synthesis from CO2 hydrogenation. We found that the activation of H adatom on the small Pd cluster and the presence of H2O on the In2O3 substrate play important roles in promoting the methanol synthesis. The hydroxyl adsorbed at the interface of Pd4/In2O3 induces the transformation of the supported Pd4 cluster from a butterfly structure into a tetrahedron structure. This important structure change not only indicates the dynamical nature of the supported nanoparticle catalyst structure during the reaction but also shifts the final hydrogenation step from H2COH to CH3O.},
doi = {10.1016/j.jcat.2014.06.002},
journal = {Journal of Catalysis, 317:44-53},
number = ,
volume = ,
place = {United States},
year = {Fri Aug 01 00:00:00 EDT 2014},
month = {Fri Aug 01 00:00:00 EDT 2014}
}
  • Methanol synthesis from CO2 hydrogenation on the defective In2O3(110) surface with surface oxygen vacancies has been investigated using periodic density functional theory calculations. The relative stabilities of six possible surface oxygen vacancies numbered from Ov1 to Ov6 on the perfect In2O3(110) surface were examined. The calculated oxygen vacancy formation energies show that the D1 surface with the Ov1 defective site is the most thermodynamically favorable while the D4 surface with the Ov4 defective site is the least stable. Two different methanol synthesis routes from CO2 hydrogenation over both D1 and D4 surfaces were studied and the D4 surface was foundmore » to be more favorable for CO2 activation and hydrogenation. On the D4 surface, one of the O atoms of the CO2 molecule fills in the Ov4 site upon adsorption. Hydrogenation of CO2 to HCOO on the D4 surface is both thermodynamically and kinetically favorable. Further hydrogenation of HCOO involves both forming the C-H bond and breaking the C-O bond, resulting in H2CO and hydroxyl. The HCOO hydrogenation is slightly endothermic with an activation barrier of 0.57 eV. A high barrier of 1.14 eV for the hydrogenation of H2CO to H3CO indicates that this step is the rate-limiting step in the methanol synthesis on the defective In2O3(110) surface. We gratefully acknowledge the supports from the National Natural Science Foundation of China (#20990223) and from US Department of Energy, Basic Energy Science program (DE-FG02-05ER46231). D. Mei was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The computations were performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at Pacific Northwest National Laboratory in Richland, Washington. PNNL is a multiprogram national laboratory operated for DOE by Battelle.« less
  • The kinetics of methanol synthesis has been studied over SNM type oxide catalysts containing copper experimentally and theoretically. Various kinetic process models have been analyzed and distinguished by nonlinear estimation of parameters and by direct experiment to clarify the individual properties of each mode. A single kinetic model has been chosen; its applicability to this methanol synthesis has been demonstrated for a wide range of reaction mixtures at various temperatures and pressures.
  • Methanol synthesis from CO[sub 2]/H[sub 2] and CO/H[sub 2] has been compared over a Cu/ZnO/Al[sub 2]O[sub 3] catalyst. Methanol synthesis was much faster with CO[sub 2]/H[sub 2] than with CO/H[sub 2], particularly at low temperatures. A trace amount of CO[sub 2] improved the rates significantly. Thus it appeared that CO[sub 2] was the primary source of methanol with CO/CO[sub 2]/H[sub 2] feed. When space velocities were varied, both the previously conflicting observations on the effect of CO[sub 2]/CO composition, i.e., monotonical increase in synthesis rate vs the presence of a maximum rate as CO[sub 2] concentration increased, were observed. Themore » different conversion levels and consequent difference in surface oxygen coverage and/or water appeared to be responsible for the different effects. The more oxidized surface state of copper obtained for CO[sub 2]/H[sub 2] was more active and stable in methanol synthesis than the overreduced surface obtained for the CO/H[sub 2] feed. Due to the promotional and inhibition effects of water for CO/H[sub 2] and CO[sub 2]/H[sub 2] feeds, respectively, higher space velocities yielded higher synthesis rates for CO[sub 2]/H[sub 2] and the opposite effect was observed for the CO/H[sub 2]feed. 30 refs., 10 figs., 1 tab.« less
  • The low temperature (403 – 453K) conversions of CO:hydrogen and CO2:hydrogen mixtures (6 bar total pressure) to methanol over copper catalysts are both assisted by the presence of small amounts of water (mole fraction ~0.04%-0.5%). For CO2:hydrogen reaction mixtures, the water product from both methanol synthesis and reverse water gas shift serves to initiate both reactions in an autocatalytic manner. In the case of CO:D2 mixtures, very little methanol is produced until small amounts of water are added. The effect of water on methanol production is more immediate than in CO2:D2, yet the steady state rates are similar. Tracer experimentsmore » in 13CO:12CO2:hydrogen (with or without added water), show that the dominant source of C in the methanol product gradually shifts from CO2 to CO as the temperature is lowered. Cu-bound formate, the major IR visible surface species under CO2:hydrogen, is not visible in CO:moist hydrogen. Though formate is visible in the tracer experiments, the symmetric stretch is absent. These results, in conjunction with recent DFT calculations on Cu(111), point to carboxyl as a common intermediate for both methanol synthesis and reverse water gas shift, with formate playing a spectator co-adsorbate role.« less