Oxidative dehydrogenation of ethylene glycol into glyoxal over phosphorus-doped ferric molybdate catalyst

Test data for the catalytic oxidation of ethylene glycol (EG) into glyoxal obtained with a laboratory continuous flow tubular reactor are reported. A ferric molybdate catalyst modified with triammonium phosphate was used. Reaction parameters (temperature, contact time) affect the product distribution. The yield of glyoxal for the Fe-Mo-P catalyst was 43.3% at 88.9% conversion, whereas the corresponding values for the Fe-Mo (unmodified catalyst) were 20.5 and 97.2%. The addition of phosphorus formed a new Fe₂M₀P₁₂ phase which restrains the reaction pathway towards carbon oxides.     

The role of iodide promoter in selective oxidation of methanol to formaldehyde

The interaction of a CH₃I promoter and a commercial electrolytic silver catalyst was investigated using XPS, UPS and in situ confocal microprobe Raman spectroscopy. XPS and UPS results show evidence for formation of AgI on the surface of the silver catalyst. Interestingly, XPS results show no evidence for formation of any carbon species on the silver catalyst at room temperature, implying that CH₃I can be used as a “pure” I‐modifier in the catalytic oxidation of CH₃OH to HCHO. UPS results show a positive work function change (Δφ > 0) for the I‐modified catalysts. In situ Raman studies show that both the adsorption and reaction of methanol were promoted on the modified silver surface. The present experimental results provide not only an understanding of the surface chemistry of the silver catalyst but also a further understanding of the promotion effect of CH₃I in the selective oxidation of CH₃OH to HCHO. This revised version was published online in July 2006 with corrections to the Cover Date.     

The oxidative dehydrogenation of methanol over a novel low‐loading Ag/SiO2–TiO2 catalyst

Catalytic oxidation of methanol to formaldehyde was carried out over Ag/TiO₂-SiO₂ catalysts prepared by chemical reduction. The catalytic activity was measured at the temperature interval 820-920 K, O₂/CH₃OH molar ratio between 0.35 and 0.50 and at the space velocity of 1.2 × 10⁵ h^-1. The optimal content of silver determined by chemical analysis was about 1.7 wt%. The yield of formaldehyde over this catalyst was ~13% higher than that of the industrial pumice-supported silver catalyst and even ~3.5% higher than that of electrolytic silver. The XRD patterns for silver particles supported on TiO₂-SiO₂ are corresponding to Ag(111), (200) and (220), respectively. SEM was used to determine its morphology and particle size. Isolated silver particles were observed on the surface of the catalyst. O₂ chemisorption by using the pulse technique was carried out to determine the free silver surface areas. The average silver particle size from the calculation of selective oxygen chemisorption was found to be in good agreement with that observed from SEM. This revised version was published online in July 2006 with corrections to the Cover Date.     

In situ surface Raman spectroscopy studies of oxygen adsorbed on electrolytic silver

In situ Raman spectroscopy has been employed to investigate oxygen adsorption on electrolytic silver catalyst under industrial conditions for methanol oxidation to formaldehyde. Both adsorbed atomic and molecular oxygen species are shown to exist on the silver surface in O₂ flow above 870 K. The peroxide species is determined to be a precursor to atomic adsorbed oxygen. In consideration of the industrial process, the molecular mechanism of the partial oxidation of methanol and the adsorption mechanism of oxygen on electrolytic silver surface are discussed.     

Novel sol–gel‐derived Ag/SiO2–Al2O3 catalysts for highly selective oxidation of methanol to formaldehyde

Novel Ag/SiO₂–Al₂O₃ catalysts with low silver content prepared by the sol–gel method exhibit excellent catalytic properties in the catalytic oxidation of methanol to formaldehyde. The silver content was as low as 2% and the yield of formaldehyde was achieved as 90.3%, which is 16% higher than that of pumice‐supported silver and even 5–6% higher than that of a commercial electrolytic silver catalyst. XRD, XPS and SEM results reveal that all silver was present as Ag⁺ before catalytic reaction and was partially reduced to the metallic state after the reaction. It was also found that silver was aggregated on the surface after its reduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

乙烯环氧化助催化作用的研究——多晶银表面化学修饰法

根据多晶银(电解银)表面吸附态氧主要是吸附态原子氧和次表层溶解氧的特性,探索并证实了电解银表面具有乙烯环氧化反应活性,从而研究了Ba和Cs化合物修饰电解银表面对乙烯氧化反应的助催化作用。Ba增加了活性,Cs降低了活性,但增大了环氧乙烷的选择性;对比了负载银添加Ba和Cs化合物后的助催化性能,获得了一致的结果。表明电解银表面化学修饰可作为选择和研究Ag助催化剂的一种合理而简便的手段。     

Selective oxidation with air on metal catalysts

Oxidation of organic molecules with air on metal catalysts has been known for a long time but there has been a renewed interest in recent years because these catalytic reactions are environmentally safe and could replace stoichiometric oxidations. This paper describes several oxidation reactions conducted either at high temperatures in the gas phase or at moderate temperatures in the liquid phase; in both cases they proceed via a mechanism of oxidative dehydrogenation on the metal surface. Ethylene glycol was converted to glyoxal at 550°C on Ag/SiC catalyst with a 70% yield provided promoters were added to the reaction feed (diethylphosphite or iodine) or deposited on the catalyst (LiPO₄ or H₃PO₄). The promoters improve the conversion and selectivity by modifying the structure and the oxygen concentration on the surface of silver. Oxidation of glyoxal to glyoxylic acid, glucose to gluconic acid and glycerol to various oxygenated derivatives were conducted in water at 60°C in the presence of carbon-supported palladium or platinum catalysts. Bismuth promoter, deposited on the platinum metals by redox reaction, improves the catalyst activity by preventing over-oxidation of the metal surface and favors the oxidation of secondary alcohol functions into keto-derivatives. At higher reaction temperatures, platinum catalysts produce C-C bond rupture with the formation of carboxylic acids with smaller chains. Thus, cyclohexanol was converted into C₆, C₅, and C₄ diacids with a 45% selectivity to adipic acid on Pt/C catalysts at 150°C.     

Characterization of silver catalysts for the oxidation of methanol

The selection of a silver catalyst system for further study was determined on a basis of cost and its ability to oxidize formaldehyde selectively. In addition a silver catalyst can provide a low light off temperature for the conversion of methanol to carbon dioxide and water vapor. Silver catalysts were prepared by the deposition of solutions of silver nitrate or silver chloride on gamma alumina washcoat supported on cordierite monolith. These silver catalysts were characterized by a variety of analytical techniques including TEM, SEM, EMP, STEM, XRF, XRD and FTIR.It is concluded that the best silver catalyst is prepared by deposition of silver from a solution of silver ammnonium chloride onto a cordierite supported high surface area gamma alumina washcoat, drying at 100°C in air, followed by reduction in flowing 3% H₂ in N₂ at 500°C for 4 h. This procedure will produce a silver catalyst with highest activity, largest retention and most uniform distribution of silver. The procedure also retains the concentration of silver and the gamma phase of alumina at temperatures as high as 1000°C in air for as long as 6 h.Due to the inability of normal TEM imaqing modes to obtain silver particle size information in the presence of the small gamma alumina washcoat particles a model system was made to test the ability of a dedicated STEM to furnish that information. The model system consisted of silver particles in the range of 1 to 50 nm which had been evaporated onto a uniform thin film of alumina. High resolution X-ray maps obtained from the model system demonstrate the ability to determine location and size of silver particles > 5 nm.A number of catalysts containing noble and base metals supported on gamma alumina washcoat on a cordierite monolith have also been studied. Laboratory flow reactor studies and chassis dynamometer studies using a Mercury Lynx modified to burn neat methanol have shown the following order of activity for conversion of methanol burned in experimental or engine exhaust gas: Pd > Ag > Pt + Rh > CuO + ZnO + Cr₂O₃ > Ni.     

Ozone Decomposition Reaction over α-Alumina-Supported Silver Catalyst: Comparative Study of Catalytic Surface Reactivity

An alumina-supported silver composite system has been investigated in the reaction of heterogeneous catalytic ozone decomposition. Perlite loaded with silver and silver modified zeolites have also been tested as catalysts for gas phase conversion of ozone to molecular oxygen. The catalysts have been activated by calcination and the changes occurring on the catalytic surface as a result of the reaction have been characterized in details using XPS. The SEM analysis has revealеd the role of surface morphology in the process of ozone decomposition on the surface of Ag/α-Al₂O₃ catalyst. A catalytic cycle is proposed that supports the hypothesis about the important role of the peroxide species as intermediates participating in the process and catalyzing the complete ozone conversion into molecular oxygen. It has been found out that the maximum conversion degree, achieved with the alumina-supported silver system, is up to 90%.     

钒铌氧化物催化剂催化氧化乙二醛制乙醛酸

对钒铌氧化物催化氧化乙二醛制乙醛酸进行研究,考察V₂O₅、Nb₂O₅及其混合物和工艺条件如乙二醛浓度、催化剂加入量、反应温度及反应时间对反应的影响。结果表明,HNO₃+NaNO₂+Nb₂O₅体系中,在乙二醛质量分数20%、催化剂用量1 g、反应温度318 K和反应时间2 h条件下,乙二醛转化率为82%,乙醛酸选择性为79%。以SiO₂为载体,采用共沉淀法制备Nb₂O₅/SiO₂催化剂,采用N₂等温吸附-脱附和XRD对催化剂进行表征,考察Nb₂O₅负载量和催化剂用量对催化氧化乙二醛合成乙醛酸的影响,并对催化剂稳定性进行研究。结果表明,Nb2O5能提高硝酸催化氧化乙二醛体系中乙二醛转化率和乙醛酸选择性,Nb₂O₅/SiO₂比纯Nb₂O₅的催化效果更好。HNO₃+NaNO₂+Nb₂O₅/SiO₂体系中,在催化剂用量5 g、活性组分Nb₂O₅负载质量分数18%和反应时间2 h条件下,乙二醛转化率为85%,乙醛酸选择性为87%,Nb₂O₅/SiO₂的稳定性和重复使用效果均良好。     

低压氧法合成乙醛酸的改进

用少量复合催化剂SA ,使用低压氧氧化乙二醛 ,合成乙醛酸 ,乙二醛转化率≥98% ,乙醛酸收率≥ 93%。电位滴定监控反应。研究了 pH及乙二醛对合成的影响 ,得到优惠工艺条件 :介质pH <1,反应液中乙二醛含量 (起始 )≥ 16 % ,催化剂SA适量 ,氧等气体总压0 12MPa ,反应温度 4 0～ 6 0℃ ,时间 2～ 3h。     

Epoxidation of propylene by air over modified silver catalyst

Epoxidation of C₃H₆ to C₃H₆O by air was studied over a silver catalyst modified with alkali or alkaline earth chloride salts. The catalyst preparation factors and the operational conditions could affect obviously the catalytic epoxidation property of the silver catalyst. It was shown that, as a promoter of the silver catalyst, NaCl or BaCl₂ is more suitable than LiCl or NH₄Cl. The loading of NaCl should be controlled at about 3.8 wt%. Using a feed gas of 10% C₃H₆/air at a space velocity of 1.75×10⁴ h⁻¹, 18.6% C₃H₆ conversion and 33.4% selectivity to C₃H₆O were obtained at 350°C. Using a feed gas of 5% C₃H₆/air at a space velocity of 2.4×10⁴ h⁻¹, 54.0% C₃H₆ conversion and 26.3% selectivity to C₃H₆O were obtained at 390°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis, Characterization of Ag/MCM-41 and the Catalytic Performance for Liquid-phase Oxidation of Cyclohexane

Nano-scale silver supported mesoporous molecular sieve Ag/MCM-41 was directly prepared by one-pot synthesis method. The prepared sample was characterized by XRD, TEM, and N₂ sorption. The results showed that the sample of Ag/MCM-41 had no appreciable incorporation of silver into the mesoporous matrix of MCM-41 with good crystallinity, and silver nanoparticles were dispersed inside or outside of the channels in the mesoporous host. The catalytic performance of the sample for the cyclohexane liquid-phase oxidation into cyclohexanone and cyclohexanol by oxygen in the absence of solvents without inducing agents was investigated. The 83.4% selectivity to cyclohexanol and cyclohexanone at 10.7% conversion of cyclohexane was obtained over Ag/MCM-41 catalyst at 428 K for 3 h. The turn over numbers (TONs) of Ag/MCM-41 was up to 2946. The catalytic activity of Ag/MCM-41 was also compared with Ag/TS-1 as well as Ag/Al₂O₃. The results indicated that Ag/MCM-41 showed superior activity to both Ag/TS-1 and Ag/Al₂O₃. A calcined Ag/MCM-41 was found to be an efficient catalyst for the cyclohexane oxidation into cyclohexanol and cyclohexanone using oxygen as oxidant.     

In situ surface Raman spectroscopy studies on the interaction between oxygen and ethanol on electrolytic silver catalyst

In situ Raman spectroscopy is employed to investigate the oxidation of ethanol on the electrolytic silver catalyst under catalytic conditions. Over the temperature range of 300–873 K, the configuration of the surface intermediates is detected. The ethoxide species, acetate species, adsorbed acetaldehyde and surface hydroxide exist on the silver surface. The mechanism for the oxidation of ethanol on the silver surface under industrial conditions is discussed and compared with that obtained in ultrahigh vacuum systems.     

Ambient temperature oxidation of carbon monoxide using a Cu2Ag2O3 catalyst

The mixed copper–silver oxide, Cu₂Ag₂O₃, has been prepared by co-precipitation and tested for ambient temperature carbon monoxide oxidation. The catalyst demonstrated appreciable low temperature oxidation activity and the catalyst aged for 4 h was the most active. Carbon monoxide conversion increased with time-on-stream, reaching steady state after ca. 1000 min. Acomparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu₂Ag₂O₃, aged for 4 h was at least as active as the hopcalite.     

Direct epoxidation of propylene to propylene oxide on various catalytic systems: A combinatorial micro-reactor study

A combinatorial approach is used to investigate several bimetallic catalytic systems and the promoter effect on these catalysts to develop highly active and selective catalysts for direct epoxidation of propylene to propylene oxide (PO) using molecular oxygen. 2%Cu/5%Ru/c-SiO₂ catalyst yielded the highest performance with high propylene conversion and PO selectivity among the bimetallic catalytic systems including silver, ruthenium, manganese and copper metals. On the other hand, the most effective catalyst and promoter in the epoxidation reaction was determined to be sodium chloride promoted Cu–Ru catalyst supported over SiO₂ with 36% selectivity & 9.6% conversion (3.46% yield) at 300 °C and 0.5 feed gas ratio (propylene/oxygen).     

Vapour phase oxidation of ethylene glycol to glyoxal on supported cupric oxide

The vapour phase oxidation of ethylene glycol to glyoxal by air was studied in a stainless steel tube reactor using cupric oxide as a catalyst on carriers such as active alumina, pumice stone, silicon carbide, ceramics and fused alumina. A catalyst containing 3 to 5% cupric oxide on pumice stone was found to be satisfactory for the process. The effects of temperature, period of reaction and concentration of ethylene glycol and oxygen on the yield and conversion to glyoxal were studied, and the most suitable conditions were determined for the process. Carbon dioxide and formaldehyde were the major by-products in the reaction. Formaldehyde was formed mainly due to the homogeneous reactions of ethylene glycol with oxygen in the void space of the reactor. The formation of glyoxal and carbon dioxide were correlated by suitable empirical rate expressions.     

Characterization by scanning tunneling microscopy of silver oxydehydrogenation catalysts

A silicon carbide-supported silver catalyst used in the oxydehydrogenation of ethylene glycol to glyoxal has been studied by scanning tunneling microscopy. The surface morphology depends upon reaction conditions. Silver particles normally sinter into large plates covering the support. However, in the presence of diethylphosphite there is a chemical erosion which results in a tortuous and fractal-like surface.     

Applications of bifunctional aldehydes to improve paper wet strength

Glyoxal and glutaraldehyde behave very differently for improving wet strength of paper. It is found that glyoxal is very efficient for improving temporary wet strength of paper without the presence of a catalyst and exposure to elevated temperatures. When a metal salt, such as Zn(NO₃)₂, is used as a catalyst and the curing temperature is increased, the durable wet strength of glyoxal‐treated paper increases at the expense of its flexibility, as shown by reduced stretch and folding endurance. Glutaraldehyde is not able to provide any improvement in wet strength to paper, even under high curing temperatures, provided no catalyst is used. With the aid of a metal salt catalyst, glutaraldehyde imparts excellent durable wet strength to paper without significantly sacrificing folding endurance, and the wet strength of glutaraldehyde‐treated paper increases steadily as curing temperature increases. The different behavior of glyoxal and glutaraldehyde may be attributed to their different reactivity toward cellulose. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2539–2547, 2002     

Novel Silver Loaded Hydroxyapatite Catalyst for the Selective Catalytic Reduction of NOx by Propene

A novel and high performance silver loaded hydroxyapatite (HAp) catalyst for the selective catalytic reduction (SCR) of NO_x by propene is reported for the first time. The catalysts with variable silver contents have been prepared and characterized extensively by different techniques such as XRD, XPS, BET-surface area, TPR, TPD and ICP analyses. The DeNO_x activities of these catalysts are measured at reaction temperature ranged from 250 to 500 °C. The 1.5 wt.% Ag/HAp is found to be best among all the catalysts studied showing about 70% conversion and 60% selectivity towards N₂ formation at 375 °C in oxygen rich atmosphere.