Mechanism of the Water–Gas Shift Reaction Catalyzed by Efficient Ruthenium‐Based Catalysts: A Computational and Experimental Study

Abstract

Supported ionic liquid phase (SILP) catalysis enables a highly efficient, Ru‐based, homogeneously catalyzed water‐gas shift reaction (WGSR) between 100 °C and 150 °C. The active Ru‐complexes have been found to exist in imidazolium chloride melts under operating conditions in a dynamic equilibrium, which is dominated by the [Ru(CO)3Cl3]− complex. Herein we present state‐of‐the‐art theoretical calculations to elucidate the reaction mechanism in more detail. We show that the mechanism includes the intermediate formation and degradation of hydrogen chloride, which effectively reduces the high barrier for the formation of the requisite dihydrogen complex. The hypothesis that the rate‐limiting step involves water is supported by using D2O in continuous catalytic WGSR experiments. The resulting mechanism constitutes a highly competitive alternative to earlier reported generic routes involving nucleophilic addition of hydroxide in the gas phase and in solution.

Acid‐Promoted Hydroformylative Synthesis of Alcohol with Carbon Dioxide by Heterobimetallic Ruthenium‐Cobalt Catalytic System

“…Calculation results exhibited the following patterns: i) CO elimination (13.45 kcal mol −1 ) was indeed more favored than eliminating Cl − from [Ru(CO) 3 Cl 3 ] − (18.60 and 27.10 kcal mol −1 ); ii) eliminating CO from [Ru(CO) 3 Cl 3 ] − was much more endothermic (13.45 kcal mol −1 for 1 to 2 ) than the formation of [RuH(CO) 2 Cl 2 ] − (1.12 kcal mol −1 for 2 to 4 ), albeit the activation energy of 13.22 kcal mol −1 for the formation of [RuH(CO) 2 Cl 2 ] − ( 3 to TS1 ). The energy patterns involving H 2 splitting on the ruthenium catalyst resembled the very recent report …”

Catalytic Semi‐Water–Gas Shift Reaction: A Simple Green Path to Formic Acid Fuel

“…A similar WGSR mechanism is proposed for the catalysis of CO/H 2 O to FA when using transition‐metal carbonyls involving Fe or Ru atoms in basic aqueous solutions in which the basic species carbonate, hydroxide, and formiate ions are involved . The formed carbonate ion (CO 3 − ) reacts with H 2 O to form OH − and CO 2 .…”

“…However, it is difficult to desorb it from the catalyst surface . Ruthenium complexes supported in SILPs have also presented higher activation energies (41–84 kJ mol −1 ) in the WGSR . Of note, neither of these catalytic systems were able to yield FA.…”

“…The first approach was to prepare supported ionic liquid phase (SILP) nanocatalysts by sol–gel processes using 1‐ n ‐butyl‐3‐(3‐trimethoxysilylpropyl)‐imidazolium cations associated with hydrophilic (acetate, SILP‐OAc) and hydrophobic [bis((trifluoromethyl)sulfonyl)amide, SILP‐NTf 2 ] anions, which have already been shown to efficiency catalyze the WGSR in the presence of ruthenium (Ru/SILP‐NTf 2 ). It is assumed that formiate species are the primary intermediates of this reaction . Hence, monometallic Ru and Fe, as well as alloyed bimetallic RuFe NPs, were prepared in the BMIm⋅NTf 2 [1‐ n ‐butyl‐3‐methyl‐1 H ‐imidazol‐3‐ium bis((trifluoromethyl)sulfonyl)amide] IL, employing chemical decomposition of Fe(CO) 5 and Ru(methylallyl) 2 (COD)complexes under a H 2 atmosphere by using similarly reported procedures (see the Supporting Information) .…”

Dual Metal Active Sites in an Ir1/FeOxSingle‐Atom Catalyst: A Redox Mechanism for the Water‐Gas Shift Reaction

“…As one of the most important industrial processes, the water‐gas shift (WGS) reaction (CO+H 2 O↔CO 2 +H 2 , Δ H =−41.1 kJ mol −1 ) is critical in producing high‐purity hydrogen for ammonia and methanol synthesis as well as in fuel cell applications . This reaction is virtually thermally reversible and can proceed on both heterogeneous and homogeneous catalysts . Since its discovery by Fontana in 1780, a number of experimental and theoretical studies have been devoted to improving the efficiency and reducing the cost of hydrogen production from WGS reaction.…”