Catalyst Property Effects on Product Distribution during the Hydrodeoxygenation of Lignin Pyrolysis Vapors over MoO₃/γ-Al₂O₃

Abstract

Hydrodeoxygenation (HDO) of three model compounds (i.e., anisole, 4-propylphenol, and 2-butanone) and real lignin pyrolysis vapors was investigated at 673 K and ∼1.7 bar of H 2 over a series of MoO 3 /γ-Al 2 O 3 catalysts with MoO 3 loadings ranging from 0 to 19 wt % as well as bulk MoO 3 . Extensive characterization revealed catalyst acidity (strength) and the degree of MoO x oligomerization as the two main parameters in determining product distribution. Strong Lewis acid sites of γ-Al 2 O 3 were found to catalyze transalkylation, dealkylation, dehydration, and condensation reactions, the latter of which also led to high coke yields (up to 50 C%). The addition of MoO 3 progressively reduced the amount of strong Lewis acid sites and generated weaker Lewis and Brønsted acid sites with lower selectivity to condensation reactions resulting in lower coke yields. The growth of MoO x domains depended on MoO 3 loading over the γ-Al 2 O 3 support. At MoO 3 loadings higher than 8 wt %, crystalline orthorhombic MoO 3 phases were found, which behaved similar to bulk MoO 3 in catalyzing hydrogenation and HDO reactions. The integration of MoO x species and acidity from the γ-Al 2 O 3 support enabled the modulation of product selectivity. This work provides information for enabling the rational design of supported MoO 3 catalysts to allow for maximizing the production of valuable chemicals (i.e., alkenes and aromatics) from HDO of lignin (or biomass) pyrolysis vapors.

MoOx-Decorated ZrO2 Nanostructures Supporting Ru Nanoclusters for Selective Hydrodeoxygenation of Anisole to Benzene

“…For supported Ru samples with higher Mo contents, the enhanced medium-strength and strong acidity mainly stemmed from the presence of more surface Mo oxide providing acidic sites. In addition, interfacial Ru δ+ sites and defective oxygen vacancies could act as adsorption sites for the NH 3 molecule …”

“…In addition, interfacial Ru δ+ sites and defective oxygen vacancies could act as adsorption sites for the NH 3 molecule. 56 3.3. Catalytic HDO Performance of Supported Ru Catalysts.…”

Mechanistic Insights into Hydrodeoxygenation of Acetone over Mo/HZSM-5 Bifunctional Catalyst for the Production of Hydrocarbons

“…These results were in correspondence with the HDO results at atmospheric hydrogen pressure, which the catalysts were almost deactivated at the end of experiments. It is believed that Bronsted acid of HZSM-5 played a dominant role in the catalytic deoxygenation of oxygenate compounds [5,9].…”

“…However, the bio-oil, produced from biomass fast pyrolysis, has a number of undesirable properties such as low stability, low heating value and high acidity [3,4]. These disadvantages are mainly caused by the high oxygen content of biomass, which hinders the crude bio-oil from integrating with the downstream upgrading process [5]. Catalytic pyrolysis using some deoxygenated catalysts such as zeolites is an attractive approach to remove excessive amount of oxygen [6][7][8].…”

“…Another major upgrading approach is catalytic hydropyrolysis (CHP) via introducing external hydrogen into catalytic pyrolysis process using hydrodeoxygenation catalysts [5]. CHP was reported to increase the yield of hydrocarbons and decrease the yield of coke [13][14][15].…”