Acid–base properties of γ-Al2O3 and MgO–Al2O3 supported gold nanoparticles

Tuning the electronic structure of Pd by the surface configuration of Al2O3 for hydrogenation reactions

The electronic interaction between a metal and a support modulates the electronic structures of supported metals and plays an important role in manipulating their catalytic performance. However, this interaction is mainly realized in heterogeneous catalysts composed of reducible oxides. Herein, we demonstrate the electronic interaction between γ-Al2O3 and η-Al2O3 with varying acid-base properties and supported Pd nanoparticles (NPs) of 2 nm in size. The strength and number of acid-base sites on the supports and catalysts were systemically characterized by FT-IR spectroscopy and TPD. The supported Pd NPs exhibit electron-rich surface properties by receiving electrons from the electron-donating basic sites on γ-Al2O3, which are beneficial for catalyzing the hydrogenation of nitrobenzene. In contrast, Pd NPs loaded on η-Al2O3 are electron-deficient because of the rich electron-withdrawing acid sites of η-Al2O3. As a result, Pd/η-Al2O3 exhibits higher catalytic activity in phenylacetylene hydrogenation than Pd/γ-Al2O3. Our results suggest a promising route for designing high-performance catalysts by adjusting the acid-base properties of Al2O3 supports to maneuver the electronic structures of metals.

Vapor-phase oxidation of cyclohexane over supported Fe-Mn catalysts: in situ DRIFTS studies

Alumina-supported Fe-Mn oxide catalysts were synthesized by the incipient wetness impregnation method. The catalysts were characterized using various characterization techniques such as surface area, XRD, H2-TPR, and Raman spectral analysis. The adsorption (Cy-H, CO2) and oxidation of cyclohexane (Cy-H) were conducted by considering the in situ DRIFTS studies. The iron-impregnated catalyst possessed a higher surface area than the manganese-impregnated catalyst. The manganese-oxides remained dispersed in the support and the iron oxides remained in the crystalline phase in the catalyst 20Fe50Mn50/Al2O3. The reduction temperature of the catalyst decreased due to the synergistic effects of the iron-manganese oxides. The catalyst 20Fe50Mn50/Al2O3 was the most active for the vapor-phase oxidation of cyclohexane at 220 °C and 1 atm pressure. The cyclohexanolate, phenolate, and unidentate carbonate species were observed during the study. The lattice oxygen of the catalyst activates the C-H bond of cyclohexane for the formation of reactive-cyclohexanol, further decomposed by dehydration and dehydrogenation.

Continuous 2-Methyl-3-butyn-2-ol Selective Hydrogenation on Pd/γ-Al2O3 as a Green Pathway of Vitamin A Precursor Synthesis

In this work, the effect of pretreatment conditions (10% H2/Ar flow rate 25 mL/min and 400 °C, 3 h or 600 °C, 17 h) on the catalytic performance of 1 wt.% Pd/γ-Al2O3 has been evaluated for hydrogenation of 2-methyl-3-butyn-2-ol in continuous-flow mode. Two palladium catalysts have been tested under different conditions of pressure and temperature and characterized using various physicochemical techniques. The catalytic performance of red(400 °C)-Pd/γ-Al2O3 and red(600 °C)-Pd/γ-Al2O3 are affected by the coexistence of several related factors like the competition between PdH and PdCx formation during the reaction, structure sensitivity, hydrogen spillover to the alumina support and presence or absence of Pd–Al species. High-temperature reduction leads to formation of Pd–Al species in addition to pure Pd. The Pd–Al species which reveal unique electronic properties by decreasing the Pdδ− surface concentration via electron transfer from Pd to Al, leading to a weaker Pd–Alkyl bonding, additionally assisted by the hydrogen spillover, are the sites of improved semi-hydrogenation of 2-methyl-3-butyn-2-ol towards 2-methyl-3-buten-2-ol (97%)—an important intermediate for vitamin A synthesis.

Nanoconfinement of metal oxide MgO and ZnO in zeolitic imidazolate framework ZIF-8 for CO2 adsorption and regeneration

Microporous materials exhibit fast CO₂ adsorption rate with possible sacrificed capacity, while CO₂ chemisorption on metal oxides is remarkable but kinetics and reactive area are critical. In order to adopt the advantages of both microporous sorbent zeolitic imidazolate framework (ZIF) and metal oxide (MO), in this research, magnesium oxide (MgO) and zinc oxide (ZnO) were doped to ZIF-8 (MO@ZIF) using infiltration and calcination processes. The powder X-ray diffraction patterns showed retained ZIF-8 integrity after MO addition. Broad MgO peaks implied well-dispersed nanoparticles, while sharp ZnO diffractions indicated oxide agglomeration, supported by the field emission transmission electron microscope images. ZIF pore size was expanded due to confined MgO without sacrificing the framework porosity. Because of nanoconfinement, the MgO@ZIF-8 room temperature CO₂ adsorption, as well as the adsorption rate constant in pseudo-second order model, were two-fold higher than expectation. In addition, the decarbonation temperature in MgO@ZIF-8 was reduced by 40 degrees. In general, it was found that metal oxide nanoconfinement in microporous zeolitic imidazolate frameworks performed improved CO₂ uptake, facilitated adsorption kinetics at ambient temperature, and lowered regeneration temperature to release CO₂.

Monitoring the Reaction Mechanism in Model Biogas Reforming by In Situ Transient and Steady-State DRIFTS Measurements

In this work, the reforming of model biogas was investigated on a Rh/MgAl₂ O₄ catalyst. In situ transient and steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were used to gain insight into the reaction mechanism involved in the activation of CH₄ and CO₂ . It was found that the reaction proceeds through of an initial pathway in which methane and CO₂ are both dissociated on Rh metallic sites and additionally a bifunctional mechanism in which methane is activated on Rh sites and CO₂ is activated on the basic sites of the support surface via a formate intermediate by H-assisted CO₂ decomposition. Moreover, this plausible mechanism is able to explain why the observed apparent activation energy of CO₂ is much lower than that of CH₄ . Our results suggest that CO₂ dissociation facilitates CH₄ activation, because the oxygen-adsorbed species formed in the decomposition of CO₂ are capable of reacting with the CH_x species derived from methane decomposition.

Alkali- and nitrate-free synthesis of highly active Mg–Al hydrotalcite-coated alumina for FAME production

Mg–Al hydrotalcite coatings have been grown on aluminaviaa novel alkali- and nitrate-free impregnation route and subsequent calcination and hydrothermal treatment.

Non-thermal plasma-treated gold catalyst for CO oxidation

Plasma under oxygen atmosphere is available for promoting the microporosity, redox properties, and the catalytic performance of gold nanoparticles.