Size Dependence of Vapor Phase Hydrodeoxygenation of m-Cresol on Ni/SiO₂ Catalysts

Abstract

Understanding the effect of metal particle size on the reactions during hydrodeoxygenation of phenolics is of great importance for rational design of a catalyst for selective control of a desirable reaction. To this end, vapor phase hydrodeoxygenation of m-cresol was studied over 5% Ni/SiO 2 catalysts with varying Ni particle sizes (2−22 nm) at 300 °C and 1 atm H 2 . The Ni particle sizes were confirmed by several characterization techniques, and the varying surface concentration of terrace, step, and corner sites with Ni particle sizes was verified by H 2 temperature-programmed desorption. Decreasing the Ni particle size from 22 to 2 nm improves the intrinsic reaction rate by 24 times and the turnover frequency (TOF) by 3 times. The TOFs for toluene and methylcyclohexanone/methylcyclohexanol formation increase by 6 and 4 times, respectively, while the TOF for CH 4 formation decreases by 3/4, indicating that smaller particles with more defect sites (step and corner) favor deoxygenation and hydrogenation while larger particles with more terrace sites favor C−C hydrogenolysis. Density functional theory study shows that the barrier for direct dehydroxylation of phenol on Ni(111), Ni(211), and defected Ni(211) decreases from 175.6 to 145.6 and then to 120.5 kJ/mol. The results indicate that a highly coordinatively unsaturated surface Ni site is responsible for C−O cleavage through facile adsorption and stabilization of −OH in the transition state, thus facilitating deoxygenation toward toluene. Our results indicate that tuning the metal particle size is an effective approach to control reactions during hydrodeoxygenation.

Enhanced Catalysis of Pt 3 Clusters Supported on Graphene for N–H Bond Dissociation

“…[23][24][25][26][27] By conducting investigations of metal cluster catalysis, extensive efforts have been made to improve the reaction activity, and it is recognized that the specific sizes and geometric/electronic structures of clusters are often crucial factors in determining the resulting mechanisms and reaction rates. [28][29][30][31][32][33] Also, the binding energies can fluctuate with increasing numbers of atoms, allowing clusters at a certain size to transform from a two-dimensional planar structure to a three-dimensional (3-D) structure (e.g., Pt 3 vs Pt 4 ), and occasionally leading to "magic" number species such as Al 13 − , Ag 13 − , and 12,[34][35][36] In many studies, clusters are supported on a selected substrate in order to evaluate the catalytic reactions in a practical way. The interaction between the metal clusters and support is a fundamental characteristic in heterogeneous catalysis and plays an essential role in elucidating the electronic structures, adsorption behavior, and catalytic activities.…”

Stabilization of Fast Pyrolysis Liquids from Biomass by Mild Catalytic Hydrotreatment: Model Compound Study

“…Another peak at about 530 • C was associated with the well-crystallized NiO [43] or highly dispersed Ni species [42]. In addition, the main peak at 686 • C can be assigned to the reduction of nickel silicate or Ni 2+ in the bulk silicate [42], which strengthened remarkably in intensity in comparison with the catalyst synthesized by incipient wetness impregnation [44]. This illustrated that the Ni/SiO 2 catalyst, which was prepared by the deposition-precipitation method, had a stronger metal-support interaction compared to the impregnation method.…”

Hydrodeoxygenation of Benzofuran over Bimetallic Ni-Cu/γ-Al2O3 Catalysts

“…As a result, the better dispersion and decreased particle size contributed to an improved HDO performance, which implied increased hydrogenation and deoxygenation. Yang et al [30] certified that smaller metal particles improved hydrogenation and deoxygenation. The selectivity to the oxygenated intermediate product Ph decreased to 2.7%.…”