Preparation of thin SnO2 layers by inorganic sol-gel process

SnO₂ sols were prepared in the following way: (1) precipitation of metastannic acid with aqueous ammonia from aqueous solutions of SnCl₄, (2) washing the precipitates with NH₄NO₃ solution and water, (3) peptization of precipitates in water, sometimes with an addition of HNO₃, at elevated temperature using mechanical stirring. In those sols, sometimes diluted with water or ethanol, substrates (glass or silica derived wafers) were dipped and withdrawn at various rates. Gel coatings were converted into crystalline SnO₂ by thermal treatment at 600°C. Coatings with thickness between 300–2000 Å were prepared.     

Characterization and reactivity of copper oxide catalysts supported on TiO2-ZrO2

A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, electron spin resonance (ESR), temperature programmed reduction (TPR), and Brunauer-Emmett-Teller specific surface area measurements. Copper dispersion and metal area were determined by N2O decomposition by the passivation method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wt % in the sample and as a crystalline CuO phase at higher Cu loadings. Copper dispersion increases with Cu loading up to 5.1 wt % and levels off at higher loadings. The XPS peak intensity ratios of Cu 2p(3/2)/Ti 2p(3/2) and Cu 2p(3/2)/Zr 3d(5/2) were compared with the copper dispersion calculated from N2O decomposition. ESR results suggest the presence of two types of copper species on the TiO2-ZrO2 support. TPR profiles reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and related to the dispersion of Cu on TiO2-ZrO2.     

Formation and oxidation mechanisms of Pd-Zn nanoparticles on a ZnO supported Pd catalyst studied by in situ time-resolved QXAFS and DXAFS

Formation and oxidation processes of PdZn nanoparticles on ZnO were successfully observed by means of in situ time-resolved X-ray absorption fine structure spectroscopy (XAFS), and the analysis of data on near-edge (XANES) and extended (EXAFS) structures revealed detailed changes in Pd during both processes. PdZn nanoparticles were formed on ZnO through a two-step scheme under a hydrogen atmosphere. The first process was the formation of metallic Pd nanoparticles, which was quickly finished within 1 s. The second process was the formation of PdZn nanoparticles, which took several tens of minutes. Oxidation of the PdZn nanoparticles also consisted of two processes. Zn atoms were oxidized prior to Pd atoms and the metallic Pd nanoparticles surrounded by ZnO were formed afterwards. Oxidation of the metallic Pd nanoparticles was scarce and very slow. According to the results of kinetic analyses, the metallic Pd surrounded by ZnO was a stable species under the oxidative atmosphere.     

Stability of semiconductor sensors based on nanosized SnO2 and Pd/SnO2

Adsorption semiconductor hydrogen sensors were created from nanosized SnO₂ and Pd/SnO₂ materials by the sol-gel method. The sensors were shown to be stable over a long time of operation.     

Structure and reactivity of Ziegler-Natta catalyst intermediates

This paper provides a survey of our recent research on chemistry that occurs among components of Ziegler-Natta catalysts. Since the amount of information regarding this topic is enormous we have focused on alkoxo compounds, which are attracting more and more attention in polymer industry. In this concept article we discuss recent studies on the inherently very complex catalyst system that involve isolation of various solid polynuclear metal-containing species, determination of their structures by X-ray crystallography, and relating their structures to the activity in polymerization. The presented research may be useful in predicting trends for the development of new single-site catalysts as well as new co-catalysts.     

Morphological study of supported thin Pd and Pd–25Ag membranes upon hydrogen permeation

Morphological change of Pd and Pd–25Ag membranes supported by V–15Ni alloy upon hydrogen permeation was investigated in the temperature range 423–673 K. The supported Pd–25Ag membrane exhibited higher resistance to hydrogen-induced cracking and grain growth than the supported Pd membrane. Long-term permeation of Pd–25Ag/V–15Ni composite membrane was carried out at 573 and 673 K for 200 h. There was no strong metallic interdiffusion between the Pd–25Ag membrane and the V–15Ni support after the long-term permeation at 573 K but small amounts of oxide had formed on the surface of Pd–25Ag membrane. Whisker and fissure-oxide morphologies were dominant on the exit and entrance side of the Pd–25Ag/V–15Ni composite membrane, respectively, accompanied by severe metallic interdiffusion after the long-term permeation at 673 K. AES and FE-SEM results revealed that metallic interdiffusion and selective oxidation of vanadium were responsible for the deterioration of Pd–25Ag membrane at 673 K. Hydrogenation–dehydrogenation of Pd and Pd–25Ag membranes supported by stainless steel and V–15Ni alloy were in situ examined by an optical microscope. The formation of hydride was uniform in the Pd/V–15Ni sample but localized in the Pd–25Ag/V–15Ni sample, suggesting that the hydrogen transfer through interface was strongly dependent on the composition of Pd alloy membranes. As for the stainless steel supported samples, both Pd and Pd–25Ag membranes had fractured.     

Structure of the CO bond on supported Pd particles: influence of size and surface state

We have investigated the surface of supported palladium particles by static secondary ion mass spectrometry (SSIMS). Pd particles were grown in situ on alumi na (oxide layer and sapphire surfaces) and stabilized by heating treatment. The particle size, density and crystallographic structure were determined in previous studies by transmission electron microscopy and diffraction (TEM and TED). Various ionic species are detected by SSIMS analysis which makes it possible to characterize the CO absorbed layer: Pd _n CO⁺ (n=1, 2) for molecular adsorption and Pd _n C⁺ for CO dissociation. The size dependence of the bonding state of CO (linear, bridge, ...) was monitored by: PdCO⁺/σ _n Pd _n CO⁺ signal ratio over various size particles (mean diameter in the 2–9 nm range). Investigations were performed as a function of CO coverage (adsorption at room temperature) and also under CO dissociation conditions: heating under CO atmosphere or CO+O₂ (catalysis). The data analysis shows that on clean Pd particles smaller than 3 nm the CO molecules give rise mainly to PdCO⁺ species. We have interpreted this result by the adsorption of CO on two palladium atoms, the carbon end being tightly bonded to a low coordination Pd atom and the oxygen end weakly bonded to a neighbour Pd atom. These couples of Pd atoms form the specific sites for CO dissociation, the density of which depends on the roughness of the particle surface.     

Nitrogen-doped carbon-modified titanium oxides supported Pd catalyst for the electrooxidation of formic acid

Journal of Solid State Electrochemistry - A Pd catalyst supported on a composite containing nitrogen-doped carbon-modified titanium oxides (Pd/NC-Ti-O), and was prepared for formic acid...     

Pd supported on graphene modified g-C3N4 hybrid: a highly efficient catalyst for hydrogenation of nitroarenes

Graphitic carbon nitride (g-C₃N₄) and graphene (GO) have been greatly utilized as supports in the field of heterogeneous catalysis. In this work, layered C₃N₄ polymer/graphene hybrid (CNNS/rGO₂₀) with heterostructure was fabricated by a hydrothermal method followed by loading Pd nanoparticles on the hybrid. The palladium was well dispersed uniformly (1.31 nm) owing to the layered and porous heterostructure of CNNS/rGO₂₀. The obtained catalyst was used for the transfer hydrogenation of a series of nitro-compounds to give the corresponding aromatic amines with outstanding activity by employing formic acid as hydrogen donor under mild conditions. The catalytic activity of the heterogeneous catalyst showed no significant loss after five continuous use.     

Pd nanoparticles supported on CeO2 as efficient catalyst for hydrogen generation from formaldehyde solution at room temperature

A facile and efficient method for facilitating hydrogen generation from formaldehyde aqueous solution was developed using Pd nanoparticles supported on CeO₂ (Pd/CeO₂) as the catalyst. The prepared Pd/CeO₂ catalyst exhibited 100% H₂ selectivity and excellent catalytic activity for formaldehyde dehydrogenation with the initial rate of 2089 ml min⁻¹ g_Pd⁻¹ at room temperature and atmospheric pressure without any extra additive. The prepared catalyst was stable and reusable, and its catalytic activity kept almost unchanged after it was reused for the fifth run. Therefore, it is considered that this Pd/CeO₂ based hydrogen generation system may serve as an alternative hydrogen supply candidate for practical application.     

Characterization of Pd/TiO2 embedded in multi-walled carbon nanotube catalyst with a high photocatalytic activity

Pd particles loading on TiO₂-embedded multi-walled carbon nanotubes (MWCNTs), MWCNTs, and TiO₂ particles were prepared via an impregnation method with palladium(II) chlorate solution followed by heat treatment at high temperature. To characterize the catalysts, BET surface area, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were employed. The prepared catalysts were tested in degradation of methyl orange under visible light. Pd/TiO₂-MWCNTs catalyst demonstrates the highest photocatalytic activity, and the phase transformation from PdO to Pd0 phase takes place at heat treatment of embedded TiO₂. The nanoparticles size of TiO₂ can be decreased by introduction of MWCNTs species. Combining structural characterization with kinetic study results we could conclude that the superior catalytic performance could arise due to the Pd/TiO₂-MWCNTs catalyst’s structure.     

Enhanced reactivity of Pt nanoparticles supported on ceria thin films during ethylene dehydrogenation

The adsorption and reaction of ethylene on Pt/CeO(2-x)/Cu(111) model catalysts were studied by means of high resolution photoelectron spectroscopy (HR-PES) in conjunction with resonant photoemission spectroscopy (RPES). The dehydrogenation mechanism is compared to the HR-PES data obtained on a Pt(111) single crystal under identical conditions. It was found that the Pt nanoparticle system shows a substantially enhanced reactivity and several additional reaction pathways. In sharp contrast to Pt(111), partial dehydrogenation of ethylene on the supported Pt nanoparticles already starts at temperatures as low as 100 K. Similar to the single crystal surface, dehydrogenation occurs via the isomer ethylidene (CHCH(3)) and then mainly via ethylidyne (CCH(3)). In the temperature region between 100 and 250 K there is strong evidence for spillover of hydrocarbon fragments to the ceria support. In addition, splitting of ethylene to C(1) fragments is more facile than on Pt(111), giving rise to the formation of CH species and CO in the temperature region between 250 and 400 K. Upon further annealing, carbonaceous deposits are formed at 450 K. By heating to 700 K, these carbon deposits are completely removed from the surface by reaction with oxygen, provided by reverse spillover of oxygen from the ceria support.     

ZnO纳米线负载Pd1单原子催化剂催化若干反应性能的考察

将孤立的Pd原子分散到ZnO纳米线(NWs)上作为单原子催化剂(SACs),并考察了它们在若干反应中的催化性能.Pd1/ZnO SAC对甲醇蒸汽重整制氢反应表现出高的活性、稳定性和CO2选择性.该催化剂体系对CO和H2的氧化也具有高活性,但在富氢物料中CO优先氧化反应中的催化剂性能较差,这主要是由于在ZnO负载的Pd1原子上H2氧化的强竞争反应所致.常压下在Pd1/ZnO SAC上就可发生逆水汽变换反应.该系列催化反应测试结果清楚地表明,选择合适金属与载体对开发分子催化转化用单原子催化剂至关重要.     

Surface roughness and electrical conductivity of the SnO2 ultra‐thin layers investigated by X‐ray reflectivity

Spray pyrolysis technique was applied to deposit two sets of ultra‐thin layers of tin dioxide (SnO₂). For the first and second sets, 0.01 and 0.05 molar precursor solutions were prepared, respectively. In both sets, utilizing the X‐ray reflectivity (XRR) technique, the effect of precursor concentration (PC) and precursor volume (PV) on the layer structure are investigated. The layer thickness of the samples, in each set, is a PV‐dependent parameter. For the same PV, samples with higher PC have a larger thickness and higher density. The electron density profiles deduced from XRR data analyses establish a link between measured values of sheet resistance and electron densities. The samples with higher PV and PC show less sheet resistance. The quantum size effect was utilized to show that the surface roughness for layers of more than almost 200 Å of samples in set two plays no role in the layer conductivity. Meanwhile, the same effect explains, adequately, the role of the surface roughness in the resistivity of the ultra‐thin layers in Set 1.     

纳米复合氧化物CuO·SnO2的制备与结构表征

0引言由于纳米材料在热学、电学、磁学、光学等方面具有的独特性能,使其在新功能材料、催化、光电能转换等许多领域引起了人们浓厚的研究兴趣[1]。近年来,纳米催化剂对固体推进剂的燃烧性能影响研究已成为热点[2～9]。但是由于固体推进剂燃烧的特殊性,要求不仅提高燃速,而且降低压力指数,因此并非所有的纳米催化剂都是有效的。大量实践已证明[10],多种催化剂的复合使用,将可获得远远优于单一催化剂的效果。研究已发现[11],纳米复合氧化物是由多种元素复合而成,使其在结构和性能上得到互补和叠加,加上纳米粒子所具有的各种效应,从而产生独特…     

草簇状石墨烯片限域Pd纳米粒子及其催化应用(英文)

通过氨基离子液体改性石墨烯,并将其固载于堇青石表面,作为负载型Pd催化剂的载体.所制备的Pd催化剂经加氢老化后,表面石墨烯呈草簇状结构,将Pd纳米粒子限域于片层内,有效防止了Pd的流失和团聚.在重要的工业反应对羧基苯甲醛(4-CBA)加氢中,此结构催化剂与传统的钯碳催化剂相比,表现出很好的稳定性     

Factors influencing decomposition of H2O2 over supported Pd catalyst in aqueous medium

Since H₂O₂ decomposition can result in selectivity/yield loss in the direct H₂O₂ synthesis process from H₂ and O₂ over supported Pd catalysts, it is important to have an enhanced understanding about the factors affecting the H₂O₂ decomposition reaction. Herein, detailed studies have been undertaken to investigate the influence of different factors, such as (a) nature and concentration of acid in reaction medium, (b) nature and concentration of halide in presence and absence of acid in reaction medium, (c) pretreatment procedures and (d) catalyst modification by incorporation of different halides, on the H₂O₂ decomposition reaction over a 5% Pd/C catalyst in aqueous medium at 25 °C. This study has shown that the H₂O₂ decomposition activity is profoundly influenced by all the above factors. The effectiveness of the acids in suppressing the H₂O₂ decomposition activity decreased in the following order: hydroiodic acid > hydrobromic acid > hydrochloric acid  acetic acid > phosphoric acid > sulfuric acid > perchloric acid. The ability of the acid to decrease the H₂O₂ decomposition activity was found to very strongly depend on the nature of its associated anion. Halides, such as iodide, bromide and chloride were particularly effective in suppressing the H₂O₂ decomposition activity. Oxidation pretreatment of the catalyst was found to strongly suppress its H₂O₂ decomposition activity, while a reduction treatment was found to promote its activity. A gradual decrease in the H₂O₂ decomposition activity of the catalyst was observed with each successive usage due to in situ sub-surface oxidation of Pd by H₂O₂. Halide incorporation either via the reaction medium or prior catalyst modification had a similar qualitative effect on the H₂O₂ decomposition activity.     

Structure and reactivity of Ru nanoparticles supported on modified graphite surfaces: a study of the model catalysts for ammonia synthesis

Supported ruthenium metal catalysts have higher activity than traditional iron-based catalysts used industrially for ammonia synthesis. A study of a model Ru/C catalyst was carried out to advance the understanding of structure and reactivity correlations in this structure-sensitive reaction where dinitrogen dissociation is the rate-limiting step. Ru particles were grown by chemical vapor deposition (CVD) via a Ru(3)(CO)(12) precursor on a highly oriented pyrolytic graphite (HOPG) surface modified with one-atomic-layer-deep holes mimicking activated carbon support. Scanning tunneling microscopy (STM) has been used to investigate the growth, structure, and morphology of the Ru particles. Thermal desorption of dissociatively adsorbed nitrogen has been used to evaluate the reactivity of the Ru/HOPG model catalysts. Two different Ru particle structures with different reactivities to N(2) dissociation have been identified. The initial sticking coefficient for N(2) dissociative adsorption on the Ru/HOPG model catalysts is approximately 10(-6), 4 orders larger compared to that of Ru single-crystal surfaces.