Mechanisms of selective cleavage of C-O bonds in di-aryl ethers in aqueous phase

Jiayue He, Chen Zhao, Donghai Mei, Johannes A. Lercher

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109 Scopus citations

Abstract

A route for cleaving the C-O aryl ether bonds of p-substituted H-, CH 3-, and OH- diphenyl ethers has been explored over Ni/SiO2 catalyst at very mild conditions (393 K, 0.6 MPa). The C-O bond of diphenyl ether is cleaved by parallel hydrogenolysis and hydrolysis (hydrogenolysis combined with HO* addition) on Ni. The rates as a function of H2 pressure from 0 to 10 MPa indicate that the rate-determining step is the C-O bond cleavage on Ni surface. H* atoms compete with the organic reactant for adsorption leading to a maximum in the rate with increasing H2 pressure. In contrast to diphenyl ether, hydrogenolysis is the exclusive route for cleaving a C-O bond of di-p-tolyl ether to form p-cresol and toluene. 4,4′-Dihydroxydiphenyl ether undergoes sequential surface hydrogenolysis, first to phenol and OC6H4OH * (adsorbed), which is then cleaved to phenol (C 6H4OH* with added H*) and H2O (O* with two added H*) in a second step. Density function theory supports the operation of this pathway. Notably, addition of H* to OC6H4OH * is less favorable than a further hydrogenolytic C-O bond cleavage. The TOFs of three diaryl ethers with Ni/SiO2 in water follow the order 4,4′-dihydroxydiphenyl ether 69molmolNi Surf-1h -1 > diphenyl ether 26molmolNi Surf-1h-1 > di-p-tolyl ether 1.3molmolNi Surf-1h-1, in line with the increasing apparent activation energies, ranging from 4,4′-dihydroxydiphenyl ether (93 kJ mol-1) < diphenyl ether (98 kJ mol-1) < di-p-tolyl ether (105 kJ mol-1).

Original languageEnglish
Pages (from-to)280-290
Number of pages11
JournalJournal of Catalysis
Volume309
DOIs
StatePublished - 2014

Keywords

  • Aqueous phase reaction
  • DFT calculation
  • Lignin-derived ethers
  • Selective C-O cleavage

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