Activity Of Metal Oxide Catalysts Research Articles

Insights into the role of water and surface OH species in methane activation on copper oxide: a combined theoretical and experimental study

An integrated theoretical and experimental investigation reveals how the presence of water alters the activity of metal oxide catalysts in gas-phase activation and conversion of methane.

Highly-efficient degradation of ensulizole using monopersulfate activated by nanostructured cobalt oxide: A comparative study on effects of different nanostructures

The most extensively used sunscreen protecting agent, Ensulizole, has been proven to exhibit hormone disrupting effects. To establish efficient processes to destruct Ensulizole in water, SO4•−-involved advanced oxidation processes using monopersulfate (MPS) seem useful. Since cobalt (Co) is the most capable of metal for activating MPS, Co3O4 appears as a promising heterogeneous catalyst for activating MPS to degrade Ensulizole. As catalytic activities of metal oxide catalysts are strongly associated with their morphologies, and surficial properties, nanoscale Co3O4 with functional nanostructures would be expected as advantageous catalysts for activating MPS. Therefore, three Co3O4 materials with distinct nanostructures and shapes were fabricated in this study, including Co3O4 cone ball (COCB), Co3O4 plate lump (COPL), and Co3O4 needle sheaf (CONS). Their surficial properties are also noticeably distinct with different fractions of Co2+, and Co3+, various oxygen vacancies, textural features and surface defects. Through comparing these three nanostructured Co3O4 for activating MPS to degrade Ensulizole, CONS exhibits the tremendously higher catalytic activity than COCB and COPL for activating MPS to eliminate Ensulizole completely and rapidly. The Ea value of Ensulizole degradation of CONS is also significantly low as 9.8 kJ/mol, which is the lowest Ea ever reported in literatures. CONS could also retain its catalytic activities over 5 continuous cycles to rapidly degrade Ensulizole. The activation mechanism of MPS by CONS and Ensulizole degradation pathway are also comprehensively elucidated via experimental evidences and the theoretical calculation to offer insightful information of development of Co-based heterogeneous catalysts for Ensulizole degradation.

Transition‐Metal‐Doped α‐MnO2 Nanorods as Bifunctional Catalysts for Efficient Oxygen Reduction and Evolution Reactions

AbstractNano‐sized α‐MnO2 nanorods doped with Co or Ru were directly synthesized using a continuous hydrothermal synthesis process (production rate 10 g h−1) and investigated as relatively inexpensive (due to the small Ru content) bifunctional catalysts for both the Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER). The materials were extensively characterized using a range of analytical methods; these including Extended X‐Ray Absorption Fine Structure (EXAFS) spectroscopy measurements, which was accompanied by density functional theory studies, in order to elucidate the role of dopants in α‐MnO2 structure. Electrochemical ORR and OER investigations of the as‐prepared doped α‐MnO2 nanomaterials were compared to more expensive Pt/C or RuO2 catalysts. The doped manganese oxide nanomaterials were used as bifunctional catalysts in the positive electrode of zinc air batteries (with oversized zinc metal negative electrode and limited density of discharge window) and displayed excellent performance (the overpotential was 0.77 and 0.68 V for α‐MnO2 modified with 7.6 at% Co and 9.4 at% Ru, respectively). Overall, as a result of doping, this study achieved improved bifunctional catalytic activities of metal oxide catalysts, which was comparable to more expensive alternatives.

Combined theoretical and experimental study on alcoholysis of amides on CeO2 surface: A catalytic interplay between Lewis acid and base sites

Alcoholysis of amides on the CeO2 surface is investigated from density functional theory (DFT) computations, in situ FT-IR spectroscopy, and catalytic studies. The thermodynamically stable amide bonds are effectively activated by the CeO2 catalyst under mild conditions in contrast to other metal oxide catalysts. DFT calculations demonstrated that acetamide adsorbed on the CeO2 surface is attacked by lattice oxygen to give a tetrahedral intermediate in the rate-determining step of the most favorable pathway. This is consistent with the experimental finding that the activity of metal oxide catalysts increases with an increase of the base strength of the catalyst. The strong base sites of CeO2 are the most important factor for the high reactivity. Interestingly, the nucleophilic attack of lattice oxygen is further assisted by the moderately strong Ce4+ Lewis acid sites. Our computational results show that the high reactivity is ascribed to a catalytic interplay between the Lewis base and acid pair sites on the CeO2 surface.

Effect of the matrix composition on the activity of metal oxide catalysts in CVD synthesis of carbon nanotubes

Citrate-nitrate method was used to synthesize (Fe,Co)/MgO-Al2O3, (Fe,Mo)/MgO-Al2O3, and (CoMo)/MgO-Al2O3 catalysts for production of carbon nanotubes. Multi-walled nanotubes were formed on these catalysts by catalytic pyrolysis of a propane-butane mixture.

Activities of γ-Al 2 O 3 -Supported Metal Oxide Catalysts in Propane Oxidative Dehydrogenation

The activities of metal oxide catalysts in propane oxidative dehydrogenation to propene have been studied. The catalysts are M/γ-Al2O3 (where M is an oxide of Cr, Mn, Zr, Ni, Ba, Y, Dy, Tb, Yb, Ce, Tm, Ho or Pr). Both transition metal oxides (TMO) and rare-earth metal oxides (REO) are found to catalyze the reaction at 350-450 °C, 1 atm and a feed rate of 75 cm3/min of a mixture of C3H8, O2 and He in a molar ratio of 4:1:10. Among the catalysts, Cr-Al-O is found to exhibit the best performance. The selectivity to propene is 41.1% at 350 °C while it is 54.1% at 450 °C. Dy-Al-O has the highest C3H6 selectivity among the REO. At 450 °C, the other catalysts show C3H6 selectivity ranging from 16.2 to 37.7%. In general TMO show higher C3H6 selectivity than REO, which, however, show higher C2H4 selectivity. An attempt is made to correlate propane conversion and selectivity to C3H6 with metal-oxygen bond strength in the catalysts. For the TMO a linear correlation is found between the standard aqueous reduction potential of the metal cation of the respective catalyst and its selectivity to propane at 11% conversion. No such correlation has been found in the case of REO. Analyses of the product distributions suggest that for TMO propane activation the redox mechanism seems to prevail while the REO activate it by adsorbed oxygen.