Abstract
Hydrodeoxygenation (HDO) is one of the promising catalytic routes for converting biomass derived molecules to high value products. A key step of HDO is the cleavage of an aromatic C–O bond to accomplish the deoxygenation step, however, which is energetically unfavorable. Herein, we report a series of palladium (Pd)-incorporated α-phase of molybdenum carbide (α-MoC) mesoporous composites for enhanced HDO activity of a biomass model molecule, anisole. The catalysts, x%Pd/α-MoC (x% is the molar ratio of Pd/Mo), were investigated by X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD), Brunauer–Emmett–Teller (BET), Raman, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. Pd is highly dispersed on α-MoC when x% ≤ 1%, but aggregate to form nanoparticles when x% = 5%. The x%Pd/α-MoC catalysts (x% ≤ 1%) show enhanced HDO activity in terms of turnover frequency (TOF) and apparent activation energy barrier (Ea) compared with α-MoC and β-Mo2C catalysts. The TOF of 1%Pd/α-MoC catalyst at 160 °C is 0.115 h−1 and the Ea is 48.2 kJ/mol. Moreover, the direct cleavage of aromatic C–O bond is preferred on 1%Pd/α-MoC catalyst. The enhanced HDO activity is attributed to superior H2 dissociation ability by the highly dispersed Pd sites on carbide. This work brings new insights for rational design of the catalyst for selective C–O bond activation.
Highlights
Energy demand and increasingly environmental concerns push the society to explore clean and renewable energy stock as an alternative to fossil fuels [1]
The x%Pd/α-phase of molybdenum carbide (α-molybdenum carbide (MoC)) catalysts were prepared by temperature programed carburization
The results show that the effect between Pd sites and α-MoC sites
Summary
Energy demand and increasingly environmental concerns push the society to explore clean and renewable energy stock as an alternative to fossil fuels [1]. Lignocellulose derivatives can be upgraded to valuable products such as biofuels and chemical intermediates by catalytic removal of the oxygen-containing functional group [2,3,4,5]. A key step of the catalytic process is hydrodeoxygenation (HDO) reaction which has been widely studied in recent years [6,7]. The dissociation and cleavage of aromatic C–O bond is an essential step in HDO, but unfavorable in energetics because the bond energy of aromatic. The alkyl C–O bond cleavage usually occurs prior to aromatic C–O bond dissociation upon catalytic condition in a practical HDO process, despite the cleavage of the alkyl C–O bond not being needed for HDO of oxygen containing aromatic compounds (Scheme 1)
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