Yuexiang Zhu

Low-temperature hydrogenation of the CO bond of propanal over Ni–Pt bimetallic catalysts: from model surfaces to supported catalysts

The hydrogenation of propanal is used as a probe reaction to correlate the activity of CO bond hydrogenation over Ni–Pt bimetallic surfaces and catalysts. Density functional theory (DFT) calculations predict that propanal is more weakly bonded on the Pt–Ni–Pt(111) subsurface structure than on either Ni or Pt, suggesting a possible novel low-temperature hydrogenation pathway based on a previous trend predicted for CC hydrogenation. Surface science studies using temperature programmed desorption (TPD) on Ni-modified polycrystalline Pt foil verify that different bimetallic surface structures exhibit distinct CO hydrogenation activity, with the Pt–Ni–Pt subsurface structure being much more active for propanal hydrogenation. Furthermore, γ-Al2O3 supported Ni–Pt bimetallic catalysts have been prepared to extend the surface science studies to real world catalysis. In the gas phase hydrogenation of propanal, both batch and flow reactor studies show that Ni–Pt/γ-Al2O3 bimetallic catalysts exhibit enhanced CO hydrogenation activity compared to the corresponding monometallic catalysts. The excellent correlation between theoretical predictions, surface science studies on model surfaces, and catalytic evaluation of supported catalysts demonstrates the feasibility to rationally design bimetallic catalysts with enhanced hydrogenation activity.

Preparation and Catalytic Activity of Monolayer-Dispersed Pt/Ni Bimetallic Catalyst for C=C and C=O Hydrogenation

Abstract The monolayer-dispersed Pt/Ni bimetallic catalyst was prepared through a simple replacement reaction, and its catalytic activity for the hydrogenation of cyclohexene, styrene, acetone, and butyl aldehyde was also tested. The Pt/Ni catalyst that was prepared by the replacement reaction showed much higher activity than Pt/Ni and Pt/Al 2 O 3 catalysts with the same Pt loading prepared by the conventional impregnation method.

Promoting Low‐Temperature Hydrogenation of CO Bonds of Acetone and Acetaldehyde by using Co–Pt Bimetallic Catalysts

The catalytic hydrogenation of carbonyl groups is one of the most useful and widely applicable reaction routes for organic synthesis. For instance, the selective hydrogenation of the C=O bond in a,b-unsaturated aldehydes to unsaturated alcohols is of growing interest for the production of fine chemicals. More recently, C=O bond hydrogenation has been considered as an important initial step in catalytic conversion of cellulose biomass. Owing to the toxicity of many a,b-unsaturated aldehydes and the complex structures of cellulose, in the current study, we use acetone and acetaldehyde as probe molecules to identify novel bimetallic catalysts for the low temperature (between 308 and 343 K) hydrogenation of carbonyl groups. In addition to being a useful probe reaction, acetone hydrogenation is also an important reaction that can be used to produce 2-propanol and methyl isobutyl ketone. 7] Furthermore, the facile hydrogenation of acetaldehyde and acetone is of interest for use in the ethanol-acetaldehydehydrogen and isopropanol-acetone-hydrogen chemical heatpump systems. Bimetallic catalysts often show properties that differ distinctly from those of the parent metals, offering the opportunity to obtain novel catalysts with enhanced activity and/or selectivity. 10] Many investigations have been performed to correlate the electronic and catalytic properties by combining fundamental surface-science studies and theoretical calculations. For example, it has been demonstrated that a Pt-terminated Pt-Co-Pt(111) surface, which represents a subsurface bimetallic structure with Pt on the topmost surface layer and Co residing in the subsurface region, shows a much higher activity for the hydrogenation of cyclohexene than a Co-terminated Co-Pt-Pt (111) surface and corresponding monometallic surfaces. 14] The low temperature hydrogenation pathway on the subsurface of these bimetallic structures has been correlated to the presence of weakly bonded adsorbates, owing to the modification of the electronic properties of Pt by the subsurface Co atoms. 14] More recently, these surface science results have been extended to g-Al2O3-supported bimetallic Co–Pt catalysts, which exhibit significantly higher activity than monometallic Co and Pt catalysts for the hydrogenation of cyclohexene, benzene, and butadiene at low temperatures. The main objective of the present work is to extend the C=C hydrogenation activity of g-Al2O3 supported Co–Pt bimetallic catalysts to the low temperature hydrogenation of the carbonyl group by using batch and flow reactors. Similar to the correlation established previously for the hydrogenation of C=C bonds, the facile C=O bond hydrogenation on Co–Pt can also be correlated to the weaker binding energies of acetone and acetaldehyde on the bimetallic surface, as determined by using density functional theory (DFT) calculations. The hydrogenation activity of acetone over the Co–Pt bimetallic and Co and Pt monometallic catalysts in batch reactor studies is compared in Figure 1. The sum of gas-phase concen-

Phosphorous-Modified TiO2 with Excellent Thermal Stability and Its Application to the Degradation of Pollutants in Water

The phosphorous-modified TiO2 (P-TiO2) was synthesized by a hydrothermal method. The as-prepared P-TiO2 was evaluated for the degradation of methylene blue, the dechlorination of 4-chlorophenol, and the inactivation of Escherichia coli. In all these experiments, P-TiO2 shows superior activity compared with pure TiO2 and even better activity than the commercially available P25 in most cases. By carrying out methylene blue degradation in the presence of different scavengers, ·OH radicals were found to be the dominant reactive oxidizing species. The excellent performance of P-TiO2 was correlated with its pronounced ability to generate ·OH radicals under illumination. We also found that P-TiO2 is extraordinarily stable against annealing. Its transformation from anatase to rutile does not occur until calcination as high as 950 °C. This phase transformation is retarded since the phosphate species on the surface of the particles acts as a barrier to grain boundary nucleation. This peculiar feature of P-TiO2 gives it reliable performance during water decontamination even after calcination at 900 °C since it retains a 100% anatase phase at this stage.

Isotopic Studies of Sn-Cr Binary Oxide Catalysts for Methane Total Oxidation

A series of Sn-Cr binary oxide catalysts were prepared by a co-current co-precipitation method and tested for methane total oxidation. The binary oxide catalysts have much higher surface areas and catalytic activities for methane oxidation than pure SnO2. CrOx/SnO2 with a Cr/Sn atomic ratio of 3:7 displays the highest activity. Selected samples were subjected to temperature-programmed 18O isotope-exchange measurements. Both complete and partial heteromolecular 18O isotope exchange, as well as oxygen release, was observed for all catalysts. Reaction between CH4 and 18O2 under static conditions was performed to investigate the reaction mechanism and it was found that the total oxidation of methane over Sn-Cr binary oxide catalysts occurs via a redox cycle with the chromium ion in a high oxidation state as the active center. Oxygen mobility of the catalyst plays an important role in the total oxidation of methane, but too high a mobility leads to very high oxygen release and a reduction of the surface reoxidability. This causes a decrease in the catalytic oxidation activity.