Methanol synthesis by the hydrogenation of CO2 over Zn-deposited Cu(111) and Cu(110) surfaces

The hydrogenation of CO₂ over Zn-deposited Cu(111) and Cu(110) surfaces was performed at 523 K and 18 atm using a high pressure flow reactor combined with XPS apparatus. It was shown that the ZnO _x species formed on Cu(111) during reaction directly promoted the methanol synthesis. However, no such promotional effect of the Zn was observed for methanol formation on Cu(110). Thus, Zn on Cu(111) acts as a promoter, while Zn on Cu(110) acts as a poison. The activation energy and the turnover frequency are in fairly good agreement with those obtained for Cu/ZnO powder catalysts.     

CO oxidation on a Cu(100) catalyst

The oxidation of carbon monoxide by molecular oxygen on a single crystal Cu(100) catalyst was studied at 458 K using reactant gas mixtures with CO/O₂ ratios of 2/1, 10/1 and 25/1 at a total pressure of 10 Torr. The catalytic activities were found to be strongly dependent upon the CO/O₂ ratio. Under stoichiometric reaction conditions (CO/O₂ = 2), the initial CO oxidation activity decreased sharply; with a highly reducing reaction mixture (CO/O₂ = 25), the initial activity gradually increased. These changes in catalytic activities with reactant gas mixture composition correlate with changes in surface composition, namely an increase in the surface oxygen coverage. Post-reaction TPD revealed the presence of a carbonate-like species which decomposed at ca. 630 K.     

CO oxidation on a model Cu/Rh(100) catalyst

The reaction between carbon monoxide and molecular oxygen on a model Cu/Rh(100) bimetallic catalyst was studied at 455 K using a CO/O₂ = 2 reactant gas mixture at a total pressure of 10.0 Torr. A maximum in the initial activity was observed at a Cu coverage of 1.3 monolayers. However, the Cu overlayers were found to be unstable at the reaction conditions employed in that the Cu films interact strongly with surface oxygen to form three-dimensional CuO_x clusters. The morphological modifications were found to influence markedly the catalytic properties of the surface. However, the initial catalytic activity and surface morphology of the Cu films could be restored by flashing the sample to > 750 K.     

Interaction of carbon dioxide with clean and oxygenated Cu(110) surfaces

Thermal desorption studies of CO₂ adsorbed on Cu(110) at 85 K and low pressures reveal nearly 100% dissociation on the oxygen-free surface to give adsorbed oxygen and CO. By oxygen predosing a pronounced molecular adsorption state at 100 K is induced with up to a twenty-fold coverage increase, which cannot be explained by simply considering the dissociation equilibrium on the surface. Probably new sites are generated by oxygen as indicated by a pronounced increase of the sticking coefficient. The adsorbed amount of CO₂ in dependence on oxygen dose at 85 K exhibits a maximum, which is tentatively attributed to the dynamics of the surface due to oxygen induced reconstruction ((1×1) p(2×1)). On polycrystalline copper enhanced CO₂ dissociation is observed.     

Adsorption states of carbon monoxide on oxygenated Cu(110) faces

Oxygen preadsorption on Cu(110) surfaces strongly reduces the CO desorption peak at 220 K, typical for clean Cu(110) and induces the development of less tightly bound states, which probably correspond to sites on Cu(111) micro-facets, formed in the course of oxygen stimulated surface reconstruction. A smaller part of the CO molecules ( 20%) seems to interact with adsorbed oxygen to give adsorbed CO ₂ ^– which can be stabilized in the presence of CO₂ by formation of van der Waals complexes, e.g. [CO₂ · CO ₂ ^– ]. At increasing temperature this complex decomposes or disproportionates to give desorbing CO and adsorbed CO ₃ ^– . The interpretation is tentative, but some evidence is given to it by TDS from Cu(111), by XPS, STM and SIMS studies and by theoretical calculations.     

Negative activation energies in CO oxidation over an icosahedral Au/Mg(OH)2 catalyst

In the course of our studies on CO oxidation over Au/Mg(OH)₂ we have discovered a catalyst which exhibits an apparent negative activation energy when studied under ultra‐dry conditions (80 ppb moisture content). A review of current literature suggests that the oxidation of CO may occur by a reaction between CO and OH radicals and not by oxygen as previously thought. Substantial differences in catalytic behaviour between low and high temperature suggest that the reaction is complex and that more than one reaction pathway is present. This revised version was published online in July 2006 with corrections to the Cover Date.     

Density Functional Study of the CO Oxidation on a Doped Rutile TiO2(110): Effect of Ionic Au in Catalysis

We used density functional theory to examine whether doping oxides makes them better oxidation catalysts. We studied in detail titania doped with Au and used CO oxidation as a test of the oxidizing power of the system. We show that doping with Au, Ag, Cu, Pt, Pd, Ni reduces dramatically the bond of surface oxygen to titania or ceria, making them better oxidation catalysts. These calculations suggest that it is worthwhile to explore doped oxides as oxidation catalysts.     

Shedding light on catalytic ignition: coverage changes during CO oxidation on Pd(110)

Catalytic ignition or ‘light-off’ has been studied for a reaction of importance in automobile exhaust emissions, namely, CO oxidation over Pd, a metal which has become an important component of car catalysts. We present kinetic and spectroscopic studies to show that light-off is associated with a step change in surface composition of reactants as the surface is heated. Fast XPS using synchrotron radiation of high brightness reveals that the surface is dominated by CO at low temperature and the coverage suddenly switches during light-off to an oxygen-atom-dominated situation. This revised version was published online in August 2006 with corrections to the Cover Date.     

HREELS investigations of trans-dichloroethene adsorption and chemical reaction on Cu(110)

The chemisorption and reaction of trans-dichloroethene on Cu(110) have been investigated by high-resolution electron-energy-loss spectroscopy (HREELS) as a function of coverage and temperature. At 135 K, both physisorbed and chemisorbed trans-dichloroethene are present. Heating to 200 K leads to the formation of acetylene and of a partially dehalogenated intermediate species. By 300 K, the acetylene trimerises to form adsorbed benzene at the surface. Adsorption of trans-dichloroethene at 300 K produces benzene directly. Evidence of C–Cl cleavage at temperature as low as 220 K is clearly marked by the emergence of very intense Cu–Cl stretching vibrations which remain even after further heating up to 570 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cu-Zr-Ce-O复合氧化物催化剂上CO选择性氧化性能

将共沉淀法制备的Cu-Zr-Ce-O复合氧化物催化剂应用于富氢气体中CO的选择性氧化反应,研究了ZrO₂掺杂量及预处理方法对催化剂性能的影响,并通过H₂-TPR、CO-TPR等手段对催化剂进行了表征.结果表明,掺杂ZrO₂的Cu₁Zr₁Ce₉O_δ催化剂在160～200℃之间具有99％以上的CO转化率和相对较高的选择性.掺杂适量的ZrO₂能够提高催化剂的热稳定性和储氧能力,促进催化剂表面吸附氧向晶格氧的转化.经氧气预处理的Cu₁Zr₁Ce₉O_δ催化剂活性最高.催化剂上Cu⁺/Cu²⁺氧化还原离子对和表面的晶格氧含量均影响催化剂的活性,但在富氢气氛下,表面的晶格氧对催化剂的性能影响较大.     

CO Oxidation Studied Using ‘Fast’ XPS and a Molecular Beam Reactor

We have combined the use of a molecular beam reactor with ‘fast’ XPS in order to correlate changes in the rate of CO oxidation with the coverages of the adsorbates and intermediates on the surface. In the reactor CO oxidation exhibits an isothermal ‘light-off’ phenomenon in which the rate autocatalytically increases with time. This is due to the desorption of CO which releases extra sites for O₂ dissociation which, in turn, removes more CO, and hence the self-acceleration. In effect the reaction can be written as 2CO_a + O_2g + 2S → 2CO_2g + 4S, the acceleration coming from the release of extra adsorption sites, S, which are involved in the reaction itself. ‘Fast XPS’, carried out in-situ during the course of the reaction, shows domination of the surface by CO_a below 390 K and by O_a above that temperature, with a rapid change in surface coverage over a very narrow temperature window. This is an advance on earlier work, since our measurements are made in a single, continuous experiment, due to the high brightness of the synchrotron source. This also allows the data to be obtained at high energy resolution, in the presence of both gases, and without contamination. On high surface area samples this acceleration is further reinforced due to a rapid temperature increase because of the highly exothermic nature of the overall reaction.     

Promotion through gas phase induced surface segregation: methanol synthesis from CO, CO2 and H2 over Ni/Cu(100)

We have studied the rate of methanol formation over Cu(100) and Ni/Cu(100) from various mixtures of CO, CO₂ and H₂. It is found that the presence of submonolayer quantities of Ni leads to a strong increase in the rate of methanol formation from mixtures containing all three components whereas Ni does not influence the rate from mixtures of CO₂/H₂ and CO/H₂, respectively. The influence of the partial pressures of CO and CO₂ on the rate indicates that the role of CO is strictly promoting. From temperature-programmed desorption spectra it follows that the surface concentration of Ni depends strongly on the partial pressure of CO. In this way the increase in reactivity is interpreted as a CO-induced structural promotion introduced by the stronger bonding of CO to Ni as compared to Cu. It is suggested that this type of promotional behavior will be of general importance in existent catalysts and perhaps even more relevant in the development of new or improved bimetallic catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

CO selective oxidation in hydrogen-rich gas over platinum catalysts

The kinetics of CO oxidation in hydrogen-rich gas on Pt/mordenite (Pt/MD) or Pt/Al₂O₃ were investigated over a wide range of CO (0.4–1.8%) and O₂ concentrations (0.26–1.14%). The integral flow measurements showed that both the catalysts that could remove CO from 1% to ppm-level Pt/MD had a wider operation temperature range than Pt/Al₂O₃, especially towards lower temperatures.     

催化湿式氧化3-甲基吡啶农药废水的研究

以过渡金属Cu为主要活性组分,与过渡金属Mn复合,研制出催化湿式氧化法(CWO)处理含3-甲基吡啶农药废水的复合金属氧化物催化剂。结果表明,新制备的复合催化剂氧化活性显著提高,并有效地抑制铜的溶出。通过对氧气分压、反应温度和废水pH 等工艺条件的考察,催化湿式氧化法处理含3-甲基吡啶农药废水的适宜工艺条件为：190 ℃,氧分压1.60 MPa,pH＝8.28。在此条件下,用自制催化剂处理初始质量浓度为15 430 mg·L^－1的废水,在120 min 内,废水COD去除率达到92%,说明可生化性能良好。     

Methanol synthesis on Cu(100) from a binary gas mixture of CO2 and H2

The rate of methanol synthesis over a Cu(100) single crystal from a 1 1 mixture of CO₂ and H₂ has been measured at a total pressure of 2 bar and a temperature range of 483–563 K. At these conditions the apparent activation energy is determined to be 69 kJ mol^–1, and at 543 K the turnover rate is 2.7 × 10^–4 (site s)^–1. A kinetic model for the methanol synthesis is presented. Predictions from this model are in good agreement with the rates of methanol synthesis observed on real catalysts at industrial conditions.     

Spontaneous,random oscillations in the rate of CO oxidation over Pt/Alumina

This note reports a study of the effect of inert diluents alone or in mixtures on the well known spontaneous oscillations in CO oxidation over a Pt catalyst. Irregular oscillations were observed with a nitrogen diluent but not when this diluent was replaced by argon. Adding SF₆ at levels above 3.3% to argon induced oscillations, but when a similar level of CO₂ or H₂O was added to the argon diluent, oscillations were not found. Oscillations were observed only at the feed composition where one of the bifurcated steady states vanished.     

The role of Rh on Pt-based catalysts: structure sensitive NO + H2 reaction on Pt(110) and Pt(100) and structure insensitive reaction on Rh/Pt(110) and Rh/Pt(100)

The catalytic activity of the Pt(110) surface for the reaction of NO + H₂ was much less than that of the Pt(100) surface. However, the catalytic activity of the Rh deposited Pt(1l0) surface was almost equal to that of the Rh deposited Pt(100) surface. That is, the catalytic reaction of NO + H₂ on Pt(110) and Pt(100) surfaces is highly structure sensitive, but it changes to structure insensitive by the deposition of Rh atoms. These results are rationalized by formation of an active overlayer on the Pt(110) and Pt(100) surfaces, which is very analogous to the Rh-O/Pt-layer formed on Rh/Pt(100), Pt/Rh(100) and Pt-Rh(100) alloy surfaces during catalysis. The formation of the common overlayer of Rh-O/Pt-layer during catalysis is responsible for the structure insensitive catalysis of Rh deposited Pt-based catalysts, which is an important role of Rh in a three way catalyst.     

Au–Cu alloy nanoparticles supported on silica gel as catalyst for CO oxidation: Effects of Au/Cu ratios

Au–Cu bimetallic catalysts with Au/Cu ratios ranging from 3/1 to 20/1 were prepared on silica gel support by a two-step method. The catalysts were characterized by ICP, XRD and TEM. The results showed that, irrespective of Au/Cu ratios, all the bimetallic nanoparticles had significantly reduced particle sizes (3.0–3.6 nm) in comparison with monometallic gold catalysts (5.7 nm). Both CO oxidation and PROX reactions were employed to evaluate the catalytic activities of Au–Cu bimetallic catalysts. For CO oxidation, the alloy catalysts show non-monotonic temperature dependence showing a valley in the intermediate temperature range. The catalyst with Au/Cu ratio of 20/1 gave the highest activity at room temperature, but its activity showed the deepest valley with increasing the reaction temperature. On the other hand, the catalyst with Au/Cu ratio of 3/1 exhibited the best performance for PROX reaction. For the Au/Cu ratios investigated, the bimetallic catalysts showed superior performance to monometallic gold catalysts, demonstrating the synergy between gold and copper.     

双水杨醛缩乙二胺合铜[Cu(Salen)]/O2催化氧化安息香

以72.8%的产率合成了双水杨醛缩乙二胺合铜配合物[Cu(Salen)],用正交试验法考察了该配合物对安息香的空气氧化反应的催化作用。实验发现,在水杨醛乙二胺合铜配合物的催化下,安息香经空气氧化生成苯偶酰的产率可达87.9%。     

On the mechanism of the selective oxidation of methanol over elemental silver

We analysed previously the interaction of silver with oxygen and characterised three different atomic oxygen species. The present communication uses TPRS data to assign a chemical function to each of these three species prepared on a sample of practical electrolytic silver particles. With stationary and instationary conversion experiments close to practical conditions we confirmed the conclusions from the TPRS data also to hold qualitatively for the stationary operating catalyst. Surface oxygen was found to react in an oxydehydrogenation reaction with adsorbed methanol with a significant selectivity to total oxidation. Sub-surface oxygen catalyses the dehydrogenation of the adsorbed methanol with no selectivity to total oxidation. Dissolved atomic oxygen from the bulk replenishes both surface species via sub-surface oxygen. The interconversion of all three species at the high reaction temperatures required to overcome the barriers for the formation and motion of the various atomic oxygen species limits the overall selectivity of the formaldehyde production.