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

Journal Article · Wed Jan 01 00:00:00 EST 2014 · Journal of Catalysis

DOI:https://doi.org/10.1016/j.jcat.2013.09.012· OSTI ID:1118104

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

A novel route for cleaving the C-O aryl ether bonds of p-substituted H-, CH₃-, and OH- diphenyl ethers has been explored over Ni/SiO₂ catalysts at very mild conditions. 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. 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 an ether 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 HOC₆H₄O* (adsorbed), which is then cleaved to phenol (C₆H₅O* 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 HOC₆H₄O* is less favorable than a further hydrogenolytic C-O bond cleavage. The TOFs of three aryl ethers with Ni/SiO₂ in water followed the order 4,4'-dihydroxydiphenyl ether (69 h^-1) > diphenyl ether (26 h^-1) > di-p-tolyl ether (1.3 h^-1), in line with the increasing apparent activation energies, ranging from 93 kJ∙mol^-1 (4,4'-dihydroxydiphenyl ether) < diphenyl ether (98 kJ∙mol^-1) to di-p-tolyl ether (105 kJ∙mol^-1). D.M. thanks the support from the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) and by the National Energy Research Scientific Computing Center (NERSC). EMSL is a national scientific user facility located at Pacific Northwest National Laboratory (PNNL) and sponsored by DOE’s Office of Biological and Environmental Research.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1118104
• Report Number(s): PNNL-SA-97413; 47408; KC0302010
• Journal Information: Journal of Catalysis, Vol. 309; ISSN 0021-9517
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

Lignin dimer
DFT calculation
Selective C−O cleavage
Aqueous phase reaction
Environmental Molecular Sciences Laboratory