Silver-alumina catalyst

Meunier, F.C., Breen, J.P., Zuzaniuk, V. et al. (1999) Mechanistic aspects of the selective reduction of NO by propene over alumina and silver-alumina catalysts, J. Catal., 187, 493. 

Wichterlova, B., Sazama, P., Breen, J.P. et al. (2005) An in situ UV-vis and FTIR spectroscopy study of the effect of H2 and CO during the selective catalytic reduction of nitrogen oxides over a silver alumina catalyst, J. Catal. 235, 195. 

Eranen, K., Lindfors, L.E., Klingdted, F. et al. (2003) Continuous reduction of NO with octane over a silver/alumina catalyst in oxygen-rich exhaust gases combined heterogeneous and surface-mediated homogeneous reactions, J. Catal. 219, 25. 

Ethylene can be oxidized to ethylene oxide over a silver-alumina catalyst. Experimental data were obtained at 260 C and atmospheric pressure (Wan, Ind Eng Chem 45 234, 1951). Selected data are tabulated. Inlet... 

Jen, H.-W. Study of nitric oxide reduction over silver/alumina catalysts imder lean conditions Effects of reaction conditions and support, Catal Today, 1998, Volume 42, Issues 1-2, 37-44. 

Lindfors, L.-E., Eranen, K., Klingstedt, F. and Murzin, D.Yu. (2004) Silver/alumina catalyst for selective catalytic reduction of NOx to N2 by hydrocarbons in diesel powered vehicles. Top. Catal., 28, 185-189. 

Thomas, J.F., Lewis, S.A., Bunting, G.B., Storey, J.M., Graves, R.L. and Park, P.W. (2005) Hydrocarbon selective catalytic reduction using a silver-alumina catalyst... 

Shimizu, K., Shibata, J., Yoshida, H., Satsuma, A. and Hattori, T. (2001) Silver-alumina catalysts for selective reduction of NO by higher hydrocarbons structure of active sites and reaction mechanism. Appl. Catal. B Environ., 30, 151—162. 

Sazama, P. and Wichterlova, B. (2005) Selective catalytic reduction of NOx by hydrocarbons enhanced by hydrogen peroxide over silver/alumina catalysts. Chem. Commun, 38, 4810-4811. 

Ethylene oxide is produced in large, multitubular reactors cooled by pressurized boiling Hquids, eg, kerosene and water. Up to 100 metric tons of catalyst may be used in a plant. Typical feed stream contains about 30% ethylene, 7—9% oxygen, 5—7% carbon dioxide the balance is diluent plus 2—5 ppmw of a halogenated moderator. Typical reactor temperatures are in the range 230—300°C. Most producers use newer versions of the Shell cesium-promoted silver on alumina catalyst developed in the mid-1970s. 

Meunier, FC Zuzaniuk, V Breen, JP Olsson, M Ross, JRH. Mechanistie differenees in the selective reduction of NO by propene over eobalt- and silver-promoted alumina catalysts kinetic and in situ DRIFTS study. Catal. Today 2000, Volume 59, Issues 3-4, 287-304. 

Ethylene can be oxidized to EO over a silver-on-alumina catalyst in 1-in-diameter tubes approximately 20 ft long. A modem EO plant produces 200 tons/day, with a typical reactor consisting of 1000 tubes with an EO selectivity of 80% with a 4 1 C2H4 02 ratio at approximately 50% conversion of Oz. EO formation is mildly exothermic, while the competing complete combustion reaction... 

The preparation of precious metal supported catalysts by the HTAD process is illustrated by the synthesis of a wide range of silver on alumina materials, and Pt-, Pt-Ir, Ir-alumina catalysts. It is interesting to note that the aerosol synthesis of alumina without any metal loading results in a material showing only broad reflections by XRD. When the alumina sample was calcined to 900°C, only reflections for a-alumina were evident. The low temperature required for calcination to the alpha-phase along with TEM results suggest that this material was formed as nano-phase, a-alumina. Furthermore, the use of this material for hexane conversions at 450°C indicated that it has an exceptionally low surface acidity as evidenced by the lack of any detectable cracking or isomerization. 

In 1986, a process to produce 1 by the continuous, vapor phase oxidation of 1,3-butadiene over a silver on alumina catalyst was discovered by Monnier and Muehlbauer of the Kodak Corporate Research Laboratories (10). The process was further developed and commercialized by Eastman Chemical Company at its Longview, Texas plant (11). Following this discovery of an economical process for 1, the production of 2,5-DHF was once again of commercial interest. 

Lack of understanding of the above mentioned issues has led to intense study of not only what is happening on the atomic level, but also the design of new systems that have both higher selectivity and rates of conversion. Three main systems were studied thus far silver-alumina type catalysts, silver-modified manganese species, and silver-modified ceria (Ce02) systems. 

Silver-alumina type catalysts are by far the most widely used, especially since they are the main catalytic source in the epoxidation of ethylene. Therefore, they are readily available and already have undergone extensive studies. Many systems have sought to utilize the presence of NO (another harmful environmental species) in gas feeds. In this case, the NO species would be reduced to N2, causing oxidation of the hydrocarbon with the support of the catalyst. Studies have helped to elucidate the active species on the catalyst surface at varying temperatures and species leading to the desired products (31). Results from a recent study point to the active silver species being a [Ag O Al] bound intermediate that leads to N2 formation (32). If the silver is present in nanoparticle form, it is simply believed to be a spectator. Other work showed mixed results on the benefit of silver-based alumina systems for the oxidation of methane and higher hydrocarbons. The effect is dependent on the type of reactor system prepared (33,34). 

Al-Saleh et al. [Chem. Eng. J., 37 (1988) 35] performed a kinetic study of ethylene oxidation over a silver supported on alumina catalyst in a Betty reactor. At temperatures between 513-553 K and a pressure of 21.5 atm, the observed reaction rates (calculated using the CSTR material balance) were independent of the impeller rotation speed in the range 350-1000 rpm (revolutions per minute). A summary of the data is ... 

Figure 7.14. NOx to N2 conversion over silver on alumina catalyst depending on reactor arrangements.

Rather than survey all of the possible modifications that can be made to an alumina surface, we will focus on a subset involved in two different types of surface-catalyzed chemical reactions, namely, the partial oxidation of ethylene to ethylene oxide (EO) and hydrodesulfurization (HDS) processes. Both of these catalytic systems have functional points in common, in that alumina serves as a support (a-alumina for the EO process and 7-alumina for the HDS process) and alkali-metal salts serve as promoters for both reactions. To illustrate this commonality, this section will be divided into three parts (1) the adsorption of alkali-metal salts to 7-alumina, as reflected in the Rb and Cs solid-state NMR spectroscopy of these systems (2) the absorption of ethylene to silver supported on aluminas in the presence and absence of cesium salts, as followed by C NMR spectroscopy, and (3) the solid-state Mo NMR of fresh and reduced/ sulfided molybdena-alumina catalysts. 

The oxidation of inexpensive olefins to maleic anhydride is of economic interest, since apparently it is competitive with the oxidation of benzene to maleic anhydride in some locations. As yet, however, oxidation of C4 hydrocarbons to maleic anhydride has given only about 50 % of the theoretically possible conversion to the desired product. Bretton, Wan, and Dodge 12) examined the oxidation of several C4 olefins over silver and silver oxide catalysts, but found only traces of products other than COg and HgO. With a vanadium catalyst prepared by decomposition of ammonium metavanadate on low-area alumina, substantial yields of intermediate products were found. Longfield and Dixon 57) and Matsumoto and co-workers 156) reported similar results a summary is given in Table XIV. These reactions were usually... 

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