Abnormally large deuterium uptake on small transition metal clusters

Deuterium uptake experiments on gas phase transition metal cluster cations of Ni, Pt and Rh show that the small (< 10 Å dia.) clusters can bind many (up to 8) deuterium atoms per metal atom in the cluster, in contast to (H(D)/M)_max ratios near unity typically reported for single crystal metal surfaces and in previous uptake experiments on nickel and iron clusters [11]. Abnormally large (H(D)/M)_max ratios appear to be the rule rather than the exception for small transition metal clusters, an effect which has strong implications in chemical and catalytic processes involving hydrogen chemisorption.     

Sorption enhanced reaction for high purity products in reversible reactions

Reversible reactions (A + B = C + D) can be performed to near completion using an admixture of catalyst and sorbent that will selectively adsorb one of the reaction products. For an initially clean sorbent and a favorable adsorption isotherm and a long reactor, the adsorbed product, C, will propagate as a sharp, shock‐like front. While the adsorbed product will not move faster than this front, the second, nonadsorbed product, D, will, in principle, leave the reactor, uncontaminated. However, a parametric analysis of the two examples presented in this work, the water gas shift and the cracking of hydrogen sulfide, reveals an unexpectedly complex behavior. While assuming adsorption equilibrium the effect of the equilibrium constant, the reaction kinetics and adsorption isotherm on the reactant and product concentration profiles are simulated. It is found that desired behavior is favored by large equilibrium constants, rapid kinetics, and strong nonlinear adsorption. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5452–5461, 2017     

FT-IR and TPD studies on support-metal and promoter-metal interaction. Pt and Pd catalysts

New CO absorption bands were observed on promoted Pd and Pt catalysts and were attributed to C and O coordination of CO. The possibility of selective coverage of some metal faces by the promoter is discussed. TPD and FT-IR experiments show that the promoters stabilize an acetyl species upon adsorption of acetaldehyde.     

松节油催化异构-分子间氢转移反应集总动力学

以H2SO4-Pd/C为复合催化剂、N2为保护气研究了松节油直接异构-分子间氢转移反应的集总动力学。在消除内、外扩散影响的条件下,在线跟踪反应产物并用气相色谱法测定反应体系组成随时间的变化关系,借鉴集总思想和方法,建立了单萜烯、对孟烯结构的单环单萜烯、异构单萜烯、对伞花烃和氢化单萜烷复杂反应体系的集总动力学模型;采用Levenberg-Marquart法,以Matlab编程和SPSS软件对实验数据进行回归估算了模型参数,得到该复杂反应体系的活化能分别为77.86,80.18,71.33 kJ/mol,所建动力学模型与实验数据吻合良好。     

Gas‐solid catalytic reactions with an extended DSMC model

An algorithm of diffusive gas transport in porous solids based on random collisions of molecules (DSMC) is extended to include basic heterogeneous reaction mechanisms (adsorption, coadsorption, desorption, and reaction of gas species on the surface of the solid). With this model, we study the catalytic oxidation of CO inside highly porous nanoparticle layers in the transition regime using kinetic parameters from Pd(111) surfaces at ultra high vacuum conditions. Investigation of the reaction at different temperatures reveals a clear transition between a kinetic limit (low temperatures) and a diffusion limit (high temperatures). At high temperatures and under steady‐state conditions, the porous layer shows three distinct regions with different reaction rates (reactor poisoning, an effective reaction region, and a region with CO depletion), whose extends are determined by CO concentration and mass‐transport limitation. We expect that similar investigations help optimizing the structure of gas sensor elements based on nanoparticle layers fabricated with flame spray pyrolysis. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2092–2103, 2015     

The sticking probability of hydrogen on Ni, Pd and Pt at a hydrogen pressure of 1 bar

A technique for measurements of the sticking probability of hydrogen on metal surfaces at high (ambient) pressure is described. As an example, measurements for Ni, Pd and Pt at a hydrogen pressure of 1 bar and temperatures between 40 and 200 °C are presented. The sticking probabilities are extracted from measurements of the local gas composition over the catalytic surface, with the help of a model for the H–D exchange reaction. The sticking probability is lowest for Ni and similar for Pd and Pt. The apparent energies of desorption derived from the adsorption rates decrease in the order Ni, Pd, Pt. The transition between β- and α-phase in the H–Pd system has a significant effect on the activity for Pd.     

Application of ultramicroelectrodes in studies of homogeneous catalytic reactions—part II. A theory of quasi-first and second-order homogeneous catalytic reactions

The analytical expressions of quasi-first and second order homogeneous catalytic reactions with different diffusion coefficients at ultramicrodisk electrodes under steady state conditions are obtained by using the reaction layer concept. The method of treatment is simple and its physical meaning is clear. The relationship between the diffusion layer, reaction layer, the electrode dimension and the kinetic rate constant at an ultramicroelectrode is discussed and the factor effect on the reaction order is described. The order of a catalytic reaction at an ultramicroelectrode under steady state conditions is related not only to C^*_z/C^*_o but also to the kinetic rate constant and the dimension of the ultramicroelectrode; thus the order of reaction can be controlled by the dimension of the ultramicroelectrode. The steady state voltammetry of the ultramicroelectrode is one of the most simple methods available to study the kinetics of fast catalytic reactions.     

Oxidation of CO on hydrogen-loaded palladium

The oxidation of CO adsorbed on the surface of palladium electrodes loaded with different amounts of hydrogen was studied by single potential alteration infrared reflectance spectroscopy (SPAIRS). In the absence of hydrogen, only CO₂ was detected during anodic oxidation of CO. Adsorption of CO in the presence of hydrogen in palladium led to a more negative onset of its electrooxidation, and the formation of other products, such as ethanol and formaldehyde, as well as CO_{_2}. The results indicate that hydrogen occluded in palladium contributes to the displacement of carbon monoxide from the interface; this may assist in the continual electrooxidation of organic compounds at palladium electrodes.     

Coal liquefaction by in-situ hydrogen generation.: 2. Zinc-water model compound reactions

Model compound studies were carried out to elucidate the reaction mechanisms taking place during the liquefaction of coal with the hydrogen produced from the reaction of zinc and water. In compounds of the type Ph-(CH₂)_n-Ph the splitting of the aliphatic bridge was easier with higher n values. Ether type compounds such as diphenylether were unreactive although the C-O bond in dibenzylether was easily cleaved. Condensed ring aromatic compounds gave low conversion with hydrogenation being facilitated by an increase in ring number. Phenolic compounds such as phenol did not react well, but the reactivity increased with increase in aromatic ring size. The cleavage of the aliphatic bridge was accelerated by the OH group, for example, in the case of 4-hydroxydiphenylmethane bond scission was about 15 times higher than that of diphenylmethane. Heterocyclic compounds were unreactive.     

Front dynamics in catalytic surface reactions

A variety of pattern formation phenomena in catalytic surface reactions can be attributed to the dynamics of interfaces, or fronts, separating distinct uniform states. The states may represent surface coverages by different adsorbates or in the case of forced oscillations, different phases of oscillation. The dynamics of fronts are strongly affected by front instabilities and by diffusion anisotropy. We identify two new pattern formation mechanisms associated with different front behaviors in orthogonal directions: an ordering process by which stationary labyrinths in an isotropic system evolve into ordered stationary stripes, and confinement of isotropic spatiotemporal chaos to one space dimension, a state we term stratified chaos.     

Surface reactions on inverse model catalysts: CO adsorption and CO hydrogenation on vanadia- and ceria-modified surfaces of rhodium and palladium

Reducible transition metal oxides are well-known promoters of the hydrogenation of CO on noble metal surfaces. In this study the promotional effect of vanadia and ceria adlayers on Rh and Pd surfaces was investigated with emphasis on the effect of the oxidation state on CO adsorption and catalytic activity. Inverse supported catalysts were prepared by UHV deposition of V and Ce on the noble metal surface (Rh(111), Pd(111) or Rh foil). After oxidation and specified reduction, the reaction kinetics on polycrystalline Rh was measured at atmospheric pressure, and the molecular and dissociative chemisorption of CO on Rh(111) and Pd(111) and the methanation kinetics on Rh(111) were investigated by molecular beam techniques. On Rh(111), the probability of CO dissociation and the reaction rate are enhanced by submonolayer VO _x deposits. Local pressures between 10^-2 and 1 mbar are sufficient to drive the methanation at 573 K with measurable amounts of products, accompanied by significant restructuring of the catalyst surface. Although the reaction on Rh is generally promoted by small quantities of vanadia and ceria, the reaction rates depend strongly on the extent and temperature of hydrogen reduction. The observed increase of the reaction rate by reduction up to 673 K can be correlated to concomitant changes of the structure and composition of the VO _x deposits. If the reduction temperature is raised above 673 K, metallic V is partially dissolved in the bulk, and the resulting V/Rh subsurface alloy exhibits a particularly high activity. Contrary to vanadia, ceria islands on Rh promote the initial reaction only after a low-temperature reduction, but the activity decreases after reduction above 573 K.     

An electrochemical impedance study of hydrogen evolution and absorption on Sn-modified steel electrodes

In this work we report results related to hydrogen evolution and absorption, on AISI 1045 steel and AISI 1045 steel modified by Sn electrodeposition, in 1 M NaOH. The simulation of experimental impedance, steady-state j/E data and electrochemical permeation data in terms of the Volmer–Heyrovsky mechanism coupled to H absorption and diffusion, allowed the estimation of kinetic and transport parameters leading to an appropriate interpretation of diminished H absorption on Sn modified samples.     

Removal of dissolved oxygen from water using a Pd-resin based catalytic reactor

The removal of dissolved oxygen (DO) from water was studied experimentally in a Pd-resin base catalyst reactor using purified hydrogen gas as a reducing agent. The effects of various operating conditions, such as hydrogen and water flow rates, height of the catalytic resin bed, temperature, pH value and run time, on the removal of DO, had been studied extensively. The results shows that DO could be removed by the reactor from ppm to ppb levels at ambient temperature. Increases of temperature, H₂ gas rate and the height of the catalytic resin were helpful to improve the DO removal rate. The change of pH value from 4 to 12 resulted in no effect on DO removal. Reaction time was the key factor to control the DO removal efficiency. Only when the reaction time was longer than 2.3 minutes under the experimental conditions, could a very low DO level be achieved.     

Single gold atoms stabilized on nanoscale metal oxide supports are catalytic active centers for various reactions

Key recent findings that demonstrate that single‐gold atom sites stabilized on various oxide supports by –O bonds are the unique catalytic sites for a number of reactions, including the water‐gas shift reaction, methanol partial oxidation and steam reforming reactions, and the selective dehydrogenation of ethanol are summarized herein. Atomic dispersion of gold on various metal oxides was followed with aberration‐corrected high angle annular dark field/scanning transmission microscopy imaging and x‐ray absorption spectroscopy (XANES/EXAFS). Gold nanoparticles and subnanometer clusters are active only through their interfacial atoms directly interacting with the support, hence if present, they entail precious metal waste. From a design perspective, the important feature in these supported catalysts is the creation of many single‐site gold species anchored on the oxide support to maximize activity. Atomic gold‐centered catalyst designs afford 100% atom efficiency, and more importantly, have distinct product selectivity, different from that of extended metal surfaces. Novel experimental synthesis methods of atomically dispersed Au catalysts are discussed, which pave the way for the efficient use of precious metals, broadening the application of properly designed gold and other precious metals (Pt, Pd) to different reactions in energy conversion and green chemicals production. © 2015 American Institute of Chemical Engineers AIChE J, 62: 429–439, 2016     

咪唑类离子液体及其催化有机不对称反应

离子液体作为一种新型绿色溶剂,具有许多独特的物理化学性质,近年来逐渐被人们所认知,并发现可用在许多重要领域.本文简单介绍离子液体及其特点,重点介绍在咪唑类离子液体中典型的不对称加氢反应、不对称Michael加成反应、不对称Aldol反应、不对称烯丙基反应和不对称氟化反应.     

Isolation of intermediate compounds of catalytic reactions on single crystal surfaces

A key intermediate of the methanation reaction on nickel catalyst is a carbidic carbon. Accumulated carbidic intermediates on Ni(100) gives a p(2×2) p4g structure, whereas that on Ni(111) is too complex to be solved. A single domain carbide layer accidentally on Ni(111) allowed us to solve the structure explicitly. Comparison of the carbide layer on Ni(100) and that on Ni(111) showed that the carbon atoms are arranged by forming the same ordered structure. The carbide layers prepared on Ni(100), Ni(111) and Ni(110) have almost equal decomposition temperatures. Consequently, we can conclude that the same overlayer compound is formed on the three surfaces. Furthermore, the hydrogenation of the p4g carbide on Ni(100) occurs at almost equal rate to the turnover frequency of the catalytic methanation reaction. The structure insensitive methanation reaction on Ni(100), Ni(111) and Ni(110) is responsible for the same intermediate compound on these surfaces.The same strategy was applied to the reaction of NO with H₂ on Pd(100), Rh(100) and Pt-Rh(100) surfaces, and ac(2×2)-N overlayer was isolated on each of these. The hydrogenation of the isolatedc(2×2)-N produced predominantly NH species, which indicates slow NH species hydrogenation.     

Effect of oxygen electronic polarisability on catalytic reactions over oxides

This work examines two partial oxidation reactions over oxides (alcohols dehydrogenation to aldehydes and aldehydes esterification to esters) to determine how reaction rates can be quantitatively correlated with physical properties of the bulk catalysts. We show that while electronegativity difference, Δχ, metal–oxygen bond strength, E _M-O fail utterly, oxygen partial charge, q_O, and oxygen Madelung potential, V_Mad (O), do provide limited correlations for the set of roughly twelve oxides examined. However, oxygen electronic polarisability, α_O, does a much better job. We rationalise this finding in terms of the concept of chemical hardness in what appears to be the first successful application of this idea to oxide reactivity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular adsorption on V2O3(0001)/Au(111) surfaces

The adsorption of carbon monoxide (CO), propane (C₃H₈) and propene (C₃H₆) on V₂O₃(0001) films grown on Au(111) was studied by Temperature Programmed Desorption (TPD) and X-ray Photoelectron Spectroscopy (XPS). The “oxidized” surface (i.e., as prepared exhibiting V=O termination), the “reduced” surface (i.e., V=O groups being removed by electron irradiation), as well as the oxygen pre-covered reduced surface were investigated. Both TPD and XPS indicate that the oxidized surface has little affinity for CO adsorption, while the reduced surface readily binds CO (CO amount approx. 10 times higher). Accordingly, CO can be used to titrate the presence or absence of vanadyl oxygen (via adsorption on the vanadium atoms) but also of defects like surface oxygen vacancies. For propane and propene, desorption of the parent molecules was the major process, i.e., surface reactions were absent under the applied conditions. When oxygen was pre-adsorbed on the reduced surface, the adsorption properties resembled that of the oxidized surface, i.e., the vanadyl groups were (partially) re-established. TPD and XPS provide a handle to differentiate the binding sites on the V₂O₃ surface. Dedicated to Prof. Konrad Hayek.     

交联腐植酸负载钯催化剂对Heck反应催化性能研究

通过简单的方法制得了环氧氯丙烷交联腐植酸负载钯配合物催化剂,并通过IR、TG进行表征。该催化剂能够成功地催化芳基卤和不同取代芳基卤与丙烯酸、苯乙烯和丙烯酰胺的Heck反应。进一步研究显示:环氧氯丙烷交联腐植酸负载钯催化剂还能够催化溴苯与丙烯酸、苯乙烯和丙烯酰胺的反应,产率都达到95%以上;在62℃及催化剂钯含量为0.038%的条件下也能很好地催化碘苯与丙烯酸的反应。催化剂经过简单的分离处理重复使用7次仍然可以得到75.6%的产率。