Synergistic effect of palladium and oxygen vacancies in the Pd/perovskite catalysts synthesized by the spc method

A series of oxygen deficient perovskite supported palladium catalysts were prepared by the “solid phase crystallization'(spc) method and investigated with XRD, TPR, TPD, TEM, XPS, BET analysis and CO oxidation. It was found that Pd/perovskite catalysts synthesized by the spc method were more active for CO oxidation than the calcined LaCo 0 95 Pd 0 05 O 3, where Pd dispersed in the solid solution. H 2 reducing treatment in the spc method could yield not only high dispersed fine Pd particles on the perovskite surface but also oxygen deficient structure. In these perovskite supported Pd catalysts, oxygen vacancies adsorbed, activated and supplied oxygen to the active Pd sites, where the oxidation occurred with adsorbed CO. The high activities were due to the cooperative action of Pd and oxygen vacancies.

Enhanced visible light absorption of Bi_(2)WO_(6)/SiO_(2) with abundant adsorbed oxygen for the degradation of organic pollutant

Heterogeneous photocatalysts exhibit high catalytic efficiency in the degradation of pollutants,but their stability and repeatability is not very good and requires high structural matching.Simply by nanosizing the pure Bi_(2)WO_(6)(BWO)photocatalyst without constructing a heterojunction,there is a significant improvement in its performance,with an enhancement effect of about 2.3 times(99.43%).The high photocatalytic degradation efficiency of the material can be attributed to the enhanced light absorption effect brought by the three-dimensional inverse-opal structure SiO_(2)(IS)and the abundant surface adsorbed oxygen generated after the formation of Si–O–W bonds.In addition,the introduction of IS greatly increases the surface area of nanostructured BWO,which accelerates the charge transfer process,while the adsorbed oxygen promotes the participation of·O^(2−) in the photocatalytic reaction,thereby accelerating the consumption of photo-generated electrons and ultimately improving the separation of charge carriers.Furthermore,the matched photonic bandgap further improves the absorption and utilization of light of the material.In this work,we constructs Si–O–W bonds to obtain inverse-opal SiO_(2)/Bi_(2)WO_(6) with uniformly growth of pure phase nano BWO,which provides a feasible strategy for the preparation of high-performance pure-phase photocatalysts.

Surface microstructure-controlled ZrO_(2) for highly sensitive room-temperature NO2 sensors

The high sensitivity of room-temperature gas sensors is the key to innovation in the areas of environment,energy conservation and safety.However,metal-oxide-based sensors generally operate at high temperatures.Herein,we designed three ZrO_(2)-based sensors and explored their NO_(2)sensing properties at room temperature.ZrO_(2)with three different morphologies and microstructure were synthesized by simple hydrothermal methods.The microstructures of sensing materials are expected to significantly affect gas sensing properties.The rod-shaped ZrO_(2)(ZrO_(2)-R)displayed the advantages such as higher crystallinity,larger pore size,narrower band gap and more chemisorbed adsorbed oxygen,compared to hollow sphere-shaped ZrO_(2)(ZrO_(2)-HS),stellate-shaped ZrO_(2)(ZrO_(2)–S).The ZrO_(2)-R sensor showed the highest response towards 30 ppm NO_(2)(423.8%)at room temperature,and a quite high sensitivity of 198.0%for detecting 5 ppm NO_(2).Although ZrO_(2)-HS and ZrO_(2)–S sensors exhibited lower response towards 30 ppm NO_(2)(232.9%and 245.1%),the response time and recovery time of these two sensors are 5 s/19 s and 4 s/3 s,respectively.This work can provide a new strategy for the development of roomtemperature metal-oxide-based sensors.

Nanoporous nickel with rich adsorbed oxygen for efficient alkaline hydrogen evolution electrocatalysis

Sluggish water dissociation kinetics severely limits the rate of alkaline electrocatalytic hydrogen evolution reaction(HER).Therefore,finding highly active electrocatalysts and clarifying the mechanism of water dissociation are challenging but important.In this study,we report an integrated nanoporous nickel(np-Ni)catalyst with high alkaline HER performance and the origin of the corresponding enhanced catalytic activity.In 1 mol L^(-1) KOH solution,this np-Ni electrode shows an HER overpotential of 20 mV at 10 mA cm^(-2),along with fast water dissociation kinetics.The excellent performance is not only attributed to the large surface area provided by the three-dimensional interconnected conductive network but also from the enhanced intrinsic activity induced by the unique surface properties.Further studies reveal that the types of oxygen species that naturally form on the Ni surface play a key role in water dissociation.Remarkably,when the lattice oxygen almost disappears,the Ni surface terminates with_(ads)orbed oxygen(O_(ads)),exhibiting the fastest water dissociation kinetics.Density functional theory calculation suggests that when O_(ads)acts as the surface termination of Ni metal,the orientation and configuration of polar water molecules are strongly affected by O_(ads).Finally,the H–OH bond of interfacial water molecules is effectively activated in a manner similar to hydrogen bonding.This work not only identifies a high-performance and low-cost electrocatalyst but also provides new insights into the chemical processes underlying water dissociation,thus benefiting the rational design of electrocatalysts.

Effects of cerium doping position on physicochemical properties and catalytic performance in methanol total oxidation

The physicochemical properties of Pd and Pd-Pt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N2 adsorption-desorption, XPS and FT-IR. The catalytic performance for methanol total oxidation was examined to study the effects of Ce adding position.CeO2-Al2 O3-TiO2（CAT） catalysts that Ce is directly introduced into support show higher reactivity and CO2 selectivity than CeO2/Al2 O3-TiO2（Ce/AT） samples in which Ce is loaded by impregnation method.The characterization results reveal that the Ce doping position does not cause obvious otherness of basic crystalline phase and mesoporous structure of support. However, the Ce doping position affects the pore shapes of support and then influences the pore diameter. CAT catalysts possess more abundant adsorbed oxygen and more Ti3＋ can transform the more gaseous oxygen into the active oxygen species on the catalyst surface, which is beneficial to the reaction. The Al-O-Ti bridges in CAT facilitate the cooperation of Al and Ti species, which further speeds up the reaction rate.

Ce-promoted Mn/ZSM-5 catalysts for highly efficient decomposition of ozone

Manganese oxides supported by ZSM-5 zeolite(Mn/ZSM-5) as well as their further modified by Ce promoter were achieved by simple impregnation method for ozone catalytic decomposition. The yCe20Mn/ZSM-5–81 catalyst with 8% Ce loading showed the highest catalytic activity at relative humidity of 50% and a space velocity of 360 L/(g × hr), giving 93% conversion of 600 ppm O_(3) after 5 hr. Moreover, this sample still maintained highly activity and stability in humid air with 50%–70% relative humidity. Series of physicochemical characterization including X-ray diffraction, temperature-programmed technology(NH_3-TPD and H_(2)-TPR), X-ray photoelectron spectroscopy and oxygen isotopic exchange were introduced to disclose the structure-performance relationship. The results indicated that moderate Si/Al ratio(81) of zeolite support was beneficial for ozone decomposition owing to the synergies of acidity and hydrophobicity. Furthermore, compared with 20 Mn/ZSM-5-81, Ce doping could enhance the amount of low valance manganese(such as Mn^(2+) and Mn^(3+)). Besides, the Ce^(3+)/Ce^(4+) ratio of 8Ce20Mn/ZSM-5-81 sample was higher than that of 4Ce_(2)0 Mn/ZSM-5-81. Additionally, the synergy between the MnO_x and CeO_(2) could easily transfer electron via the redox cycle, thus resulting in an increased reducibility at low temperatures and high concentration of surface oxygen. This study provides important insights to the utilization of porous zeolite with high surface area to disperse active component of manganese for ozone decomposition.

Lattice expansion and smaller CuO_(x)CeO_(2-δ)particles formation by magnesium interaction for low temperature CO oxidation

A series of magnesia doped CuOxCeO_(2-δ)catalysts were prepared by co-precipitation followed by impregnation method and investigated for CO oxidation.The manuscript is devoted to explaining the role of MgO for the formation of active species on the CuOxCeO_(2-δ)surface.The improvement in catalytic activity is ascribed to the formation of various active species due to the interaction of magnesia with CuOxCeO_(2-δ).The catalysts were characterized by PXRD,N_(2)adsorption,H_(2)-TPR,XPS,SEM,EDS and HRTEM techniques.The Mg doped catalyst shows lattice expansion of ceria due to the formation of smaller Ce^(3+)species with oxygen vacancies.The Mg-O bond also takes part in CO activation and oxidation,which results in the increase of CO oxidation.The Mg doped CuOxCeO_(2-δ)catalyst shows improvement in low temperature activity compared with the CuOxCeO_(2-δ).