Development Of High-activity Catalysts Research Articles

Ag improves the performance of the oxygen evolution reaction by lowering the D-band center of the active site Ni

The development of high activity catalysts with excellent durability is a great challenge to realize the industrialization of electrolytic water oxygen evolution. In this work, Ag nanoparticles modified cross column nickel-iron hydroxyl oxide system (NiFeAg) nanocomposites were synthesized by a two-step strategy. Through XPS spectrum, Tafel slope, and EIS electrochemical impedance spectroscopy, it was found that Ag mainly plays a conductive role, accelerates charge transfer, and adjusts the surface electronic structure, to improve the activity of the catalyst. Impressive is the overall hydrolysis performance, with a current density of 10 mA cm−2 achieved at an overpotential of 211 mV, which shows better performance than other catalysts reported in the literature. Finally, through the theoretical calculation of the determination steps of adsorption energy and rate of oxygen-containing intermediates, it is determined that the active center of the catalyst is mainly Ni site. According to the theory of D-band center, Ag can effectively adjust the D-band center, thereby adjusting the adsorption strength of Ni sites on the surface of NiFe catalyst to adsorbent, and finally improving the OER performance of the catalyst.

In-situ regulation of acid sites on Mn-based perovskite@mullite composite for promoting catalytic oxidation of chlorobenzene

A series of Sm-Mn perovskite@mullite composites with different amounts of acid sites were successfully synthesized by regulating the level of in situ etched-surface modification. X-ray diffraction (XRD) test showed that the crystal structure of catalyst gradually changed from perovskite to perovskite@mullite composites and mullite. The characterization of temperature programmed desorption with ammonia (NH3-TPD) confirmed the acid sites on the surface of catalyst can be deployed by the in-situ modification. The temperature-programmed reduction with hydrogen (H2-TPR), and N2 adsorption–desorption showed that the surface modification also increased the reducibility, surface area, and mesoporosity of catalyst. The catalytic activities were compared by a long-term catalytic oxidation of chlorobenzene evaluation for 20 h of uninterrupted reaction at a relatively low temperature of 300 °C, and the Sm-Mn perovskite@mullite composite (SMPM-1.2) possessed the best catalytic stability. The X-ray photoelectron spectroscopy (XPS) measurement determined that the high ratios of lattice oxygen and tetravalent manganese did not improve the stability of catalyst in the catalytic oxidation of chlorobenzene, but the activities trends of samples were consistent with the change of surface (Mn4++Mn3+)/Mn2+ ratios. Meanwhile, the catalytic experiments for benzene, toluene, o-xylene and acetone showed that the as-prepared catalyst was also suitable for the efficient removal of the different types of VOCs. This work supplied a method for the further development of high activity catalysts for the removal of VOCs.

Cu Monolayer on Au/C and Pt/C for the Electrochemical Reduction of CO2 to Hydrocarbons

In the electrochemical conversion of CO2 into carbon – based fuels, one of the scientific challenges is the development of high activity catalysts to enhance the CO2 reduction at low overpotentials, yield valuable hydrocarbons at high current efficiency and diminish hydrogen evolution reaction activity. In this work, we present the design of nano-structured high surface area electrodes based on a Cu monolayer on Au or Pt nanoparticles supported on Carbon. A full monolayer of Cu was synthesized by underpotential deposition on Au or Pt nanoparticles for the electroreduction of CO2. Preliminary results shows that a full monolayer of Cu on Au or Pt nanoparticles cores exhibited an enhancement of the CO2 activity by a factor of 1.13 and 1.25, respectively, at -1.7 V vs. NHE over the native metal core nanoparticles in 0.1 M KHCO3. The Cu monolayer remains stable and intact on the carbon-supported Pt and Au nanoparticles before and after performing CO2 reduction.

The ethylene polymerization with Ziegler catalysts: fifty years after the discovery.

Fifty years ago, Karl Ziegler and his co-workers discovered the synthesis of polyethylenes at low pressures and moderate high temperatures with transition-metal catalysts of the 4th group and aluminum organic compounds as cocatalysts. The last 50 years represent a story of innovations in science and industry in the development of high-activity catalysts and processes based on a detailed understanding of all relevant chemical and physical processes on all scales. Catalysts, technologies, and products are still under further development, which shows that the potential of this polymerization process is not fully exploited. Today's targets include achieving better product properties at lower production costs and the substitution of other materials, such as glass, paper, steel, and concrete in certain fields because polyethylenes deliver better resource-saving solutions.

Olefin polymerization using supported metallocene catalysts: development of high activity catalysts for use in slurry and gas phase ethylene polymerizations

Reaction of hydroxylated silica and alumina supports with methyl aluminoxane in toluene suspension provides chemically modified supports suitable for use in slurry and gas-phase polymerizations of ethylene or propylene on treatment with a variety of metallocene dichloride complexes. In particular, aluminas derived from calcination of sol–gel precursors feature high degrees of surface hydroxylation in comparison with commercially available silica (or even alumina) of similar surface area and total porosity. This feature provides a mechanism for increasing the amount of aluminoxane on the former supports, such that commercially acceptable productivities (>10 kg PE/g support×h) are observed at relatively low, total levels of aluminoxane or other alkylaluminum compounds in slurry or gas-phase polymerizations, respectively. A variety of evidence indicates that leaching of active catalyst from these alumina supports occurs to a minor extent under slurry conditions, particularly at higher temperatures in the presence of additional aluminoxane. At lower temperatures, this does not occur to an appreciable extent but the morphology and bulk density of the polymer formed is unsuitable for use in a gas-phase process. This can be attributed to the method for synthesis of the sol–gel alumina precursor which results in irregular particles with a broad particle size distribution. Copolymerization of ethylene with 1-octene or 1-hexene results in formation of linear, low density, PE with a narrow composition distribution as revealed by temperature rising elution fractionation. These studies indicate that less comonomer is incorporated using these supported metallocene catalysts than their soluble analogues under otherwise identical conditions. Finally, some of the resins prepared under slurry conditions (and to a lesser extent in a gas-phase process), exhibit properties consistent with the presence of low levels of long-chain branching; this feature appears to be reasonably general for a variety of simple metallocene complexes.