A novel, mesoporous molybdenum doped titanium dioxide/reduced graphene oxide composite as a green, highly efficient solid acid catalyst for acetalization.

A novel, mesoporous composite of Mo doped TiO2/reduced graphene oxide is synthesized to be used as a highly efficient heterogeneous acid catalyst. The composite has a high surface area (263 m2 g-1) and a monomodal pore size distribution with an average pore diameter of 3.4 nm. A comprehensive characterization of the synthesized material was done using PXRD, Raman, BET, SEM, EDX, TEM, TGA, and XPS. The composite exhibited excellent catalytic activity (1.6 h-1 TOF, >99% GC yield, and >99% selectivity) towards acetalization of cyclohexanone at room tempertaure within 30 minutes. The catalyst was reusable up to 4 reaction cycles without any significant loss in the activity and the acidic site calculations showed that the reaction is mostly driven by the weak acidic sites on the composite.

Syntheses of ZnO with Different Morphologies: Catalytic Activity toward Coumarin Synthesis via the Knoevenagel Condensation Reaction.

Heterogeneous catalysts are preferred in fine chemical industries due to their easy recovery and reusability. Here, we report an easily scalable method of ZnO catalysts for coumarin synthesis. Nanocrystalline ZnO particles with diverse morphologies and crystallite sizes were prepared using different solvents. The change in morphology results in changes in band gaps, defects, basicity, and textural properties (surface areas, pore volumes, and pore sizes). The catalytic performances of the synthesized ZnO materials were tested using coumarin synthesis via the Knoevenagel condensation. The catalyst synthesized using methanol shows the highest activity and selectivity (conversion of 74%, selectivity of 94%) with a turnover number of 14.69. The increased activity of the ZnO synthesized in methanol is attributed to the combined effects of moderate basicity and relatively high textural properties of the sample.

Single-Doped and Multidoped Transition-Metal (Mn, Fe, Co, and Ni) ZnO and Their Electrocatalytic Activities for Oxygen Reduction Reaction.

The electrochemical oxygen reduction reaction (ORR) is the limiting half-reaction of fuel cells, which is mediated by using platinum-based catalysts. Hence, the development of low-cost, active ORR catalysts is highly required to make fuel cell technology commercially available. In this report, transition-metal (TM; Mn, Fe, Co, and Ni) single-doped and multidoped (MD) ZnO nanocrystals (ZNs) were prepared for use as ORR catalysts using a simple precipitation method. The effects of single doping and multidoping on the structure, morphology, and properties of the TM-doped ZNs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence, X-ray photoelectron microscopy, electron paramagnetic resonance, and Raman and photoluminescence (PL) spectroscopies. The XRD results reveal that synthesized ZnO samples retained a pure hexagonal wurtzite crystal structure, even at high levels of multidoping (nominal 20%). SEM analyses show that the morphology of the prepared ZNs varies with the doping elements, doping mode, and amounts of doping. The observation of peak shifting and peak intensity changes in Raman studies confirms the presence of dopants in ZnO. The PL investigation reveals that the incorporation of dopants into the ZnO structure increases the oxygen vacancies within the materials. The highest oxygen vacancies were present in Mn-doped ZnO and 15% MD ZnO among the single-doped and MD samples, respectively. Linear-sweep voltammetry studies conclude that doped ZnO shows enhanced ORR activity compared to the undoped samples. The Mn-doped ZnO and 15% MD ZnO exhibited the highest ORR activity among the prepared single-doped and MD ZN samples, respectively. In comparison, single doping showed better ORR activity than the multidoping system. The enhanced ORR activity of the synthesized ZN materials correlates with the amount of oxygen vacancies present in the samples. The enhanced activity of TM-doped ZnO suggests that these materials can be used as potential, low-cost electrocatalysts for ORR in fuel cell technology.

Synthesis of Large Mesoporous-Macroporous and High Pore Volume, Mixed Crystallographic Phase Manganese Oxide, Mn2O3/Mn3O4 Sponge.

The controlled synthesis of mixed crystallographic phase Mn2O3/Mn3O4 sponge material by varying heating rates and isothermal segments provides valuable information about the morphological and physical properties of the obtained sample. The well-characterized Mn2O3/Mn3O4 sponge and applicability of difference in reactivity of H2 and CO2 desorbed during the synthesis provide new developments in the synthesis of metal oxide materials with unique morphological and surface properties. We report the preparation of a Mn2O3/Mn3O4 sponge using a metal nitrate salt, water, and Dextran, a biopolymer consisting of glucose monomers. The Mn2O3/Mn3O4 sponge prepared at 1 °C·min-1 heating rate to 500 °C and held isothermally for 1 h consisted of large mesopores-macropores (25.5 nm, pore diameter) and a pore volume of 0.413 mL/g. Furthermore, the prepared Mn2O3/Mn3O4 and 5 mol %-Fe-Mn2O3/Mn3O4 sponges provide potential avenues in the development of solid-state catalyst materials for alcohol and amine oxidation reactions.

Synthesis and Electrocatalytic Activity of Ammonium Nickel Phosphate, [NH4]NiPO4·6H2O, and ß-Nickel Pyrophosphate, ß-Ni2P2O7: Catalysts for Electrocatalytic Decomposition of Urea.

Electrocatalytic decomposition of urea for the production of hydrogen, H2, for clean energy applications, such as in fuel cells, has several potential advantages such as reducing carbon emissions in the energy sector and environmental applications to remove urea from animal and human waste facilities. The study and development of new catalyst materials containing nickel metal, the active site for urea decomposition, is a critical aspect of research in inorganic and materials chemistry. We report the synthesis and application of [NH4]NiPO4·6H2O and ß-Ni2P2O7 using in situ prepared [NH4]2HPO4. The [NH4]NiPO4·6H2O is calcined at varying temperatures and tested for electrocatalytic decomposition of urea. Our results indicate that [NH4]NiPO4·6H2O calcined at 300 °C with an amorphous crystal structure and, for the first time applied for urea electrocatalytic decomposition, had the greatest reported electroactive surface area (ESA) of 142 cm2/mg and an onset potential of 0.33 V (SCE) and was stable over a 24-h test period.