Enhanced detection of ppb-level NO_(2)by uniform Pt-doped ZnSnO_(3)nanocubes

ZnSnO_(3) nanocubes(ZSNCs)with various Pt concentrations(i.e.,1 at%,2 at%,and 5 at%)were synthesized by a simple one-pot hydrothermal method.The microstructures of pure and Pt-doped ZSNCs were characterized by X-ray diffractometry,scanning electron microscopy,transmission electron microscopy,energy-dispersive X-ray spectroscopy,and X-ray photoelectron spectroscopy.Results showed that the pure ZSNCs have a perovskite structure with a side length of approximately 600 nm;this length was reduced to 400 nm after Pt doping.Following doping,PtO_(x)(PtO and PtO_(2)) nanoparticles with a diameter of approximately 5 nm were uniformly coated on the surface of the ZSNCs.Systematic investigation of the gas-sensing abilities of the nanocubes showed that the Pt-doped ZSNCs have excellent sensing properties toward nitrogen dioxide(NO_(2)) gas in the operating temperature range of 75-175℃.Among the sensors prepared,that based on 1 at%Pt-doped ZSNCs exhibited the best response of 16.0 toward 500 ppb NO_(2) at 125℃;this response is over 11 times higher compared with that of pure ZSNCs.The enhanced NO_(2) sensing mechanism of the Pt-doped ZSNCs may be attributed to the synergistic effects of catalytic activity and chemical sensitization by Pt doping.

Promoting Effects of Pt on the Catalytic Performance of Supported NiB Amorphous Alloy Catalysts for Benzene Hydrogenation

A support(denoted AM) was prepared using pseudo-boehmite and mordenite.Ni-B and NiPtB amorphous catalysts were prepared on the support by the impregnation method followed by chemical reduction with a KBH4 solution.And the catalysts were characterized by X-ray diffraction(XRD),environment scanning electron microscope(ESEM),inductively coupled plasma(ICP),H2-temperature programmed reduction(H2-TPR),differential thermal analysis(DTA),and BET.Benzene hydrogenation was used as a probe reaction to evaluate the effect of addition of small quantities of Pt on the NiB/AM catalyst.The results show that Pt can promote the reduction of NiO and the formation of active sites,leading to smaller catalyst particles and better dispersion of active metal particles on the support.The catalytic activity,sulfur resistance and thermal stability were remarkably improved by Pt doping of the NiB/AM catalyst.

Effects of platinum content on tribological properties of platinum/nitrogen doped diamond-like carbon thin films deposited via magnetron sputtering

Platinum(Pt)and nitrogen(N)were co-incorporated in diamond-like carbon(DLC)thin films using a magnetron sputtering system to form PtN-DLC thin films for tribological applications.The Pt content in the PtN-DLC films prepared on Si substrates was controlled by varying RF power applied to a Pt target at a fixed N2 flow rate.The tribological properties of the PtN-DLC films were investigated with respect to the Pt content in the films.The uncoated Si substrate surface tested against a steel ball of 6 mm in diameter had significant abrasive and fatigue wear,while no significant wear was found on the N-DLC coated sample surface,indicating that the N-DLC film effectively prevented its underlying Si substrate from wear.However,the incorporation of Pt in the N-DLC films reduced the wear resistance of the films by degrading sp3-bonded cross-linking structures of the films so that significant wear tracks were found on the surfaces of the PtN-DLC films.Therefore,the increased radio frequency(RF)power applied to the Pt target decreased the wear resistance of the PtN-DLC films as a result of the increased Pt content.

Effects of Pd doping on N2O formation over Pt/BaO/Al2O3 during NOx storage and reduction process

N2O is a powerful greenhouse gas and plays an important role in destructing the ozone layer. This present work investigated the effects of Pd doping on N2O formation over Pt/BaO/Al2O3 catalyst. Three types of catalysts, Pt/BaO/Al2O3, Pt/Pd mechanical mixing catalyst （Pt/BaO/Al203 ＋ Pd/Al2O3） and Pt-Pd co-impregnation catalyst （Pt-Pd/BaO/Al2O3） were prepared by incipient wetness imoreenation method. These catalysts were first evaluated in NSR activity tests using H2/CO as reductants and then carefully characterized by BET, CO chemisorption, CO-DRIFTs and H2-TPR techniques. In addition, temperature programmed reactions of NO with H2/CO were conducted to obtain further information about NzO formation mechanism. Compared with Pt/BaO/Al2O3 （Pt/BaO/Al2O3 ＋ Pd/Al2O3） produced less N2O and more NH3 during NOx storage and reduction process, while an opposite trend was found over （Pt-Pd/BaO/Al2O3 ＋ Al2O3）. Temperature programmed reactions of NO with H2/CO results showed that Pd/Al2O3 component in （Pt/BaO/Al2O3 ＋ Pd/Al2O3） played an important role in NO reduction to NH3, and the formed NH3 could reduce NOx to N2 leading to a decrease in N2O formation. Most of N2O formed over （Pt-Pd/BaO/Al2O3 ＋ Al2O3） was originated from Pd/BaO/Al2O3 component. H2-TPR results indicated Pd-Ba interaction resulted in more difficult- to-reduce PdOx species over Pd/BaO/Al2O3, which inhibits the NO dissociation and thus drives the selectivity to N2O in NO reduction.

Grain boundary boosting the thermal stability of Pt/CeO_(2)thin films

Understanding how defect chemistry of oxide material influences the thermal stability of noble metal dopant ions plays an important role in designing high-performance heterogeneous catalytic systems.Here we use in-situ ambient-pressure X-ray photoemission spectroscopy(APXPS)to experimentally determine the role of grain boundary in the thermal stability of platinum doped cerium oxide(Pt/CeO_(2)).The grain boundaries were introduced in Pt/CeO_(2)thin films by pulsed laser deposition without significantly change of the surface microstructure.The defect level was tuned by the strain field obtained using a highly/low mismatched substrate.The Pt/CeO_(2)thin film models having well defined crystallographic properties but different grain boundary structural defect levels provide an ideal platform for exploring the evolution of Pt–O–Ce bond with changing the temperature in reducing conditions.We have direct demonstration and explanation of the role of Ce^(3+)induced by grain boundaries in enhancing Pt2+stability.We observe that the Pt^(2+)–O–Ce^(3+)bond provides an ideal coordinated site for anchoring of Pt^(2+)ions and limits the further formation of oxygen vacancies during the reduction with H_(2).Our findings demonstrate the importance of grain boundary in the atomic-scale design of thermally stable catalytic active sites.