Natural kaolin-based Ni catalysts have been developed for low-temperature CO₂ methanation. The catalysts were prepared via a one-step co-impregnation of Ni and Ce onto a natural kaolin-derived metakaolin using a microwave-assisted hydrothermal method as an acid-/base-free synthesis method. The influences of microwave irradiation and Ce promotion on the catalytic enhancement including the CO₂ conversion, CH₄ selectivity, and CH₄ yield were experimentally investigated by a catalytic test of as-prepared catalysts in a fixed-bed tubular reactor. The relationship between the catalyst properties and its methanation activities was revealed by various characterization techniques including X-ray fluorescence, X-ray diffraction, Brunauer–Emmett–Teller, scanning electron microscopy, selected area electron diffraction, transmission electron microscopy, elemental mapping, H₂ temperature-programmed reduction, and X-ray absorption near-edge structure analyses. Among the two enhancement methods, microwave and Ce promotion, the microwave-assisted synthesis could produce a catalyst containing highly dispersed Ni particles with a smaller Ni crystallite size and higher catalyst reducibility, resulting in a higher CO₂ conversion from 1.6 to 7.5% and a better CH₄ selectivity from 76.3 to 79.9% at 300 °C. Meanwhile, the enhancement by Ce addition exhibited a great improvement on the catalyst activities. It was experimentally found that the CO₂ conversion increased approximately 7-fold from 7.5 to 52.9%, while the CH₄ selectivity significantly improved from 79.9 to 98.0% at 300 °C. Though the microwave-assisted synthesis could further improve the catalyst activities of Ce-promoted catalysts, the Ce addition exhibited a more prominent impact than the microwave enhancement. Cerium oxide (CeO₂) improved the catalyst activities through mechanisms of higher CO₂ adsorption capacity with its basic sites and the unique structure of CeO₂ with a reversible valence change of Ce⁴⁺ and Ce³⁺ and high oxygen vacancies. However, it was found that the catalyst prepared by microwave-assisted synthesis and Ce promotion proved to be the optimum catalyst in this study. Therefore, the present work demonstrated the potential to synthesize a nickel-based catalyst with improved catalytic activities by adding a small amount of Ce as a catalytic promoter and employing microwave irradiation for improving the Ni dispersion.

In the present work, the solvent-free hydrodeoxygenation of palm oil as a representative triglyceride model compound to diesel-like hydrocarbons was evaluated in a batch reactor using Pt-decorated MoO₂ catalysts. The catalysts with various Pt loadings (0.5–3%) were synthesized by an incipient wetness impregnation method. The metallic Pt and MoO₂ phases were detected in the XRD patterns of as-prepared catalysts after the reaction and acted as active components for the deoxygenation reactions. The XPS experiments confirmed the existence of metallic Pt and PtO_x species. The XANES investigation of Mo L₃-edge spectra elucidated a change in the valence state by the transformation of MoO₃ into MoO₂ species after the deoxygenation reaction. The TEM observation revealed the formation of Pt nanoparticles in the range of 1–3 nm decorated on MoO₂ species. The number of acid sites increased with stronger metal–support interactions on increasing the Pt loading. The catalytic performance of the MoO₂ catalyst significantly improved with a small amount of Pt decoration. However, the further increase in Pt loading did not relatively increase the deoxygenation activity due to the formation of the agglomerated Pt particles. The high performance of the decorated catalysts could be attributed to the moderate acidity from the Pt dispersed on MoO₂ toward decarbonylation and decarboxylation reactions.

The effect of Re promoter on Cu/γ-Al₂O₃ catalysts with various Cu : Re molar ratios was comprehensively investigated in comparison to the monometallic Cu/γ-Al₂O₃ and Re/γ-Al₂O₃ catalysts. The combination of Re and Cu resulted in a difficulty in reduction behavior of the Cu species, as detected using hydrogen temperature-programmed reduction, indicating that the Re promoter had stronger metal–support interactions. The acidity, as confirmed by ammonia temperature-programmed desorption, increased with the Re loading. X-ray diffraction and X-ray absorption near edge structure measurements of the spent CuRe catalyst revealed the existence of metallic Cu, Cu₂O, CuO, amorphous CuAl₂O₄, ReO₃, and NH₄ReO₄. The as-synthesized catalysts without reduction were directly utilized for the hydrogenolysis of furfural (FAL) into the fuel additive 2-methylfuran (2-MF). The highest 2-MF yield (86.4%) was accompanied by a 10.4% 2-methyltetrahydrofuran (2-MTHF) yield using the optimal Cu₁Re_0.14 catalyst under the investigated conditions (200 °C, 6 h, and 20 bar H₂). The kinetic study using furfuryl alcohol (FOL), a primary intermediate, revealed that the rate of 2-MF production for the optimal Cu₁Re_0.14 catalyst was faster than that of the Cu benchmark. These results indicated that a small amount of oxophilic Re species could promote the hydrogenolysis of the C–OH bond in FOL to form 2-MF due to the synergistic effect between the Cu and Re active species. In addition, the activity of the Cu₁Re_0.14 catalyst remained highly stable through four consecutive experiments.

Continuous hydrogenolysis of 5-hydroxymethylfurfural to 2,5-dimethylfuran is successfully developed and demonstrated using alumina-supported nickel–iron alloy catalysts with in situ observation of the structural transformation.

Cu/CaO catalysts with fine-tuned Co-doping for excellent catalytic performance of furfural (FAL) hydrogenation to furfuryl alcohol (FOL) were synthesized by a facile wetness impregnation method. The optimal Co_1.40Cu₁/CaO catalyst, with a Co to Cu mole ratio of 1.40:1, exhibited a 100% FAL conversion with a FOL yield of 98.9% at 100 °C and 20 bar H₂ pressure after 4 h. As gained from catalyst characterizations, Co addition could facilitate the reducibility of the CoCu system. Metallic Cu, Co-Cu alloys, and oxide species with CaO, acting as the major active components for the reaction, were formed after reduction at 500 °C. Additionally, this combination of Co and Cu elements could result in an improvement of catalyst textures when compared with the bare CaO. Smaller catalyst particles were formed after the addition of Co into Cu species. It was found that the addition of Co to Cu on the CaO support could fine-tune the appropriate acidic and basic sites to boost the FOL yield and selectivity with suppression of undesired products. These observations could confirm that the high efficiency and selectivity are mainly attributed to the synergistic effect between the catalytically active Co-Cu species and the CaO basic sites. Additionally, the FAL conversion and FOL yield insignificantly changed throughout the third consecutive run, confirming a high stability of the developed Co_1.40Cu₁/CaO catalyst.