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• Descriptors for oxidative coupling of methane were investigated. • Density functional theory described the actual catalysis results. • Optimum methyl radical adsorption energy was found for good catalysts. • The roles of surface oxygen species were revealed by surface characterizations. Catalytic descriptors were studied to design optimum catalysts for the oxidative coupling of methane (OCM) by combining density functional theory (DFT) calculations and actual reaction experiments. SrTiO 3 perovskite catalysts, selected for OCM, were modified using metal dopants, and their electronic structures were calculated using the DFT method. The CH 3 adsorption energy E ads (CH 3) and the oxygen vacancy formation energy E f (vac) exhibited volcano-type correlations with the C 2+ selectivity and O 2 -consumption for the formation of CO x , respectively. The optimum catalytic activity, represented by the C 2+ selectivity, was obtained for E ads (CH 3) = −2.0 to −1.5 eV, indicating that overly strong adsorption of methyl radicals (or easily dissociated C H bonds of methane) and relatively insufficient oxygen supplementation to the catalyst surface improve deep oxidation to CO and CO 2. Praseodymium (Pr)- and neodymium (Nd)-doped SrTiO 3 catalysts confirm the DFT-predicted optimum electronic structure of the OCM catalysts. [ABSTRACT FROM AUTHOR]

Lignin is a natural polymer contained in lignocellulose and is a potential feedstock for the production of phenolics or small aromatic molecules. However, lignin depolymerization is typically performed using low lignin concentrations and insufficiently active catalysts, which hinders industrial applications. To address this issue, we herein investigated the depolymerization of concentrated kraft lignin and oak-extracted organosolv lignin promoted by supported bifunctional metal (palladium)-acid catalysts and elucidated the roles of acid and metal sites. In addition to acid sites, which are known to be critical for lignin degradation, metal sites were found to be required to initiate lignin depolymerization. Palladium atoms promoted depolymerization even in the absence of acid sites, while acid site–promoted depolymerization required the presence of surface palladium atoms. Catalysts with bulk palladium particles were much more active than those with highly dispersed palladium particles, which suggested that efficient depolymerization required the bulky lignin polymer to be adsorbed on the palladium surface in a multidentate fashion. Thus, our work provides valuable insights into the mechanism of catalytic lignin depolymerization and paves the way to the industrial-scale application of this process. [Display omitted] • Lignin depolymerization by bifunctional metal (Pd)-acid catalysts is studied. • Roles of acid and metal sites in this depolymerization are elucidated. • Bulk Pd particles are more active than highly dispersed Pd particles. • Depolymerization requires multidentate lignin adsorption on the Pd surface. [ABSTRACT FROM AUTHOR]

Water, which frequently inhibits organic reactions, improves the hydrodeoxygenation activity of lignin-derived guaiacol on a bifunctional catalyst of Rh/SiO2-Al2O3 in a biphasic mixture of n-decane and water. The unique properties of subcritical water appear to promote hydrodeoxygenation, which improves the production of monooxygenates by removing more oxygen atoms of guaiacol while suppressing the formation of fully deoxygenated hydrocarbons because of the poor solubility of hydrophobic monooxygenates. [ABSTRACT FROM AUTHOR]

Abstract: In the fructose dehydration to 5-hydroxymethylfurfural (HMF) in dimethyl sulfoxide, the catalytic function of 1,3-dialkylimidazolium-based ionic liquids with different counter-anions was investigated. It was found that the effects of alkyl chain length and additional alkyl group in Cl-containing ionic liquids were negligible whereas the activity of 1-butyl-3-methylimidazolium-based ionic liquids was considerably changed by varying the anion (particularly, halide ions). The latter finding was confirmed by the control experiment result that the addition of KBr or Ca(CH3COO)2 dramatically tuned the catalytic activity of 1-butyl-3-methylimidazolium chloride. From these results and the proposed reaction pathway, it was consequently believed that 1,3-dialkylimidazolium halide contained the dual catalytic function to act as both Brönsted acid and nucleophile for the fructose dehydration to HMF. [Copyright &y& Elsevier]

Abstract: In the hydrolysis of cellobiose to glucose, the addition of 1-butyl-3-methylimidazolium chloride (BmimCl) ionic liquid (IL) enhanced the catalytic activity of Nafion® NR50 substantially. Similar results were observed with 1-butyl-2,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, and 1-butyl-3-methylimidazolium bromide and iodide, but not acetate. The glucose yield was the highest when the amount of BmimCl added equalled the number of protons available in the resin catalyst, but further addition of BmimCl did not lead to substantial changes in the glucose yield. The extent of activity enhancement did not correlate well with the extent of swelling of the Nafion® NR50 resin, but correlated well with the pH change of the reaction mixture due to the presence of ILs. It is believed that the principal contributor to the effect of ILs is displacement of the protons of the sulfonate groups in the resin by ion-exchange with imidazolium ions, and these released protons are the catalyst for the hydrolysis reaction. For the IL with acetate as the anion, the released protons associate with acetate to form acetic acid, which is a weak acid and has low hydrolysis activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na-W-Mn-Ba-Ti composite catalyst exhibited 26.0 % C 2+ yield at 700 °C. • Optimum temperature, 700 °C, is 100 °C lower than that of conventional Mn-Na 2 WO 4. • Nanostructures of catalyst adjusted the redox of Mn and W. • H 2 -TPR, TEM, XRD, Raman, and others elucidated the catalytic activity. The oxidative coupling of methane (OCM) using hybrid catalysts containing BaTiO 3 perovskite and Mn-Na 2 WO 4 exhibited high activity and high selectivity at low temperature: 66.3 % C 2+ (olefins and paraffins) selectivity and 25.9 % C 2+ yield at 700 °C which is 100 °C lower than that used for Mn-Na 2 WO 4 catalysts (800 °C). Upon the preparation of complex catalysts, the insertion of Mn into BaTiO 3 (BaTi(Mn)O 3) and the formation of Na x Mn(Ti)O 2 improved the oxygen-supplying ability of the catalysts. Additionally, strong interactions between the WO 4 2− anions and BaTi(Mn)O 3 or Na x Mn(Ti)O 2 stabilized the WO 4 2− anions on the surface and improved the methane activation ability of the catalysts for the favorable production of hydrocarbons. The nanoscopic modification of catalysts was confirmed using H 2 –temperature-programmed reduction, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy results. [ABSTRACT FROM AUTHOR]

Biogas is a promising renewable energy source; however, it needs to be upgraded to increase its low calorific value. In this study, oxidative coupling of methane (OCM) was selected to convert it to a higher fuel standard. Prior to establishing the scaled-up OCM process, the effect of organic/inorganic binders on catalytic activity was examined. The selection of the binders and composition of the catalyst pellet influenced the pore structure, fracture strength, and catalytic activity of the catalyst pellets. It was also observed that the O2 supply from the inorganic binder is a key factor in determining catalytic activity, based on which the composition of the catalyst pellets was optimized. The higher heating value increased from 39.9 (CH4, Wobbe index = 53.5 MJ/Nm3) to 41.0 MJ/Nm3 (OCM product mixture, Wobbe index = 54.2 MJ/Nm3), achieving the fuel standard prescribed in many countries (Wobbe index = 45.5–55.0 MJ/Nm3). The reaction parameters (temperature, gas hourly space velocity, size of the reaction system, and the CH4/O2 ratio) were also optimized, followed by a sensitivity analysis. Furthermore, the catalyst was stable for a long-term (100 h) operation under the optimized conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • High carbon number fuels were produced from furan by one-pot reaction. • Multifunctional catalysts were used for each step by manipulating reaction conditions. • Selective production of fuels was achieved depending Pd, Ni, and Ru. The multifunctionality of tungstate-zirconia-supported metal catalysts was demonstrated in a three-step conversion of 2-methylfuran (2-MF) into deoxygenated C 10-15 hydrocarbon fuels in a one-pot reactor, with condensation, hydrogenation, and hydrodeoxygenation performed using single tungstate-zirconia-supported metal catalysts. Manipulation of the reaction conditions, in particular, the reaction temperature and feeding reactant for each reaction step, enabled different catalytic functions of the tungstate-zirconia-supported metals at different reaction stages. Among the metals, Ni favored the production of C 10 hydrocarbons by suppressing further condensation to C 15 compounds, whereas Ru favored the trimerization of 2-MF during the condensation step to produce C 15 hydrocarbons. The superior hydrogenation of 2-MF on Pd reduced the formation of C 10-15 compounds. The acidity and hydrogenation activity of the catalysts were investigated to demonstrate the multifunctionality of tungstate-zirconia-supported metals. The catalysts were characterized using H 2 temperature programmed reduction, H 2 temperature programmed desorption, X-ray diffraction, transmission electron microscopy, and nuclear magnetic resonance; the results confirmed the variations in their activity among the different reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalytic condensation of furfural and 2-methylfuran was performed. • Several sulfonated acidic carbon catalysts were prepared with mild grafting. • Surface acidic functionalities with pKa < 4 were required for acid-mediated condensation. The catalytic condensation of furfural and 2-methylfuran was performed to produce C15 diesel precursors using sulfonated acidic carbon catalysts, including multi-walled carbon nanotubes, graphene oxide, carbon aerogel, activated carbon, and carbon black. Sulfonated multi-walled carbon nanotubes were prepared with mild sulfonate grafting procedure, and displayed negligible modification of their pore structures. They exhibited the highest turnover frequency, indicating that the acid strength, depicted by the pK a , determined the catalytic condensation activity. The pK a values of the catalysts needed to be less than 4 for enabling the condensation of furfural and 2-methylfuran, and catalysts with pK a values greater than 4 exhibited poor condensation. The pK a , or acid strength, was determined by the environment of the surface sulfonates, which were electronically modified to adjust the stability of the sulfonate anions to release protons. [ABSTRACT FROM AUTHOR]

Ru nanoparticles supported on tungstated zirconia (WZr) were prepared and used for the catalytic hydrodeoxygenation of guaiacol to deoxygenated hydrocarbon fuels. The tuning of tungsten, from 5 to 20 wt%, adjusted the number of acid sites on the tungstated zirconia and the size of the Ru nanoparticles. The optimum fraction of tungsten was determined for the optimum hydrodeoxygenation activity. The conversion of guaiacol reached a maximum of 96.8% for 10 wt% of tungsten. Increasing the tungsten fraction increased the number of acid sites and the dispersion of Ru, but the formation of tungsten oxide (WO x ) particles with too large fraction of tungsten inhibited the formation of smaller Ru nanoparticles, thus reducing the catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: A kinetic model of the oxidative coupling of methane was developed by considering ethane, ethylene, carbon monoxide, and carbon dioxide production in such a way that the reactor was designed for the reactions to take place in the catalyst-loading region as much as possible. The effectiveness of the reactor specification was validated by low conversion of methane in the blank test. A mechanism for catalytic reactions on the surface of Na2WO4/Mn/SiO2 gel and gas-phase radical reactions was suggested based on a literature survey. Reaction rates were developed by applying rapid equilibrium for adsorption and the quasi steady state approximation to the intermediate on the catalytic surface. Kinetic parameters were estimated by fitting experimental data with temperature, space velocity, and CH4/O2 ratio varied in full factorial manner. The validity of the model was corroborated by comparing its simulated results with experimental data. The effectiveness of the estimated parameters was discussed with respect to reported values. The effects of operating conditions were assessed using the developed model. [Copyright &y& Elsevier]