Oxide catalysts characterization

Beckler, R. K., and M. G. White, Polynuclear Metal Complexes as Model Mixed Oxide Catalysts Characterization , J. Catal, 102, pp. 252-256 (1986). 

Hu, H., Wachs, LE., and Bare, S.R., Surface structures of supported molybdenum oxide catalysts Characterization by Raman and Mo Lj-edge XANES, J. Phys. Chem., 99, 10897,1995. 

Kapteijn, R, van Langeveld, D., Moulijn, J.A., Andreini, A., Vuurman, M.A., Turek, A.M., Jehng, J.M., andWachs, I.E., Alumina-supported manganese oxide catalysts characterization effect of precursor and loading. J. Catal 1994,150, 94-104. 

Meta/ Oxides. The metal oxides aie defined as oxides of the metals occurring in Groups 3—12 (IIIB to IIB) of the Periodic Table. These oxides, characterized by high electron mobiUty and the positive oxidation state of the metal, ate generally less active as catalysts than are the supported nobel metals, but the oxides are somewhat more resistant to poisoning. The most active single-metal oxide catalysts for complete oxidation of a variety of oxidation reactions are usually found to be the oxides of the first-tow transition metals, V, Cr, Mn, Fe, Co, Ni, and Cu. 

In particular, emphasis will be placed on the use of chemisorption to measure the metal dispersion, metal area, or particle size of catalytically active metals supported on nonreducible oxides such as the refractory oxides, silica, alumina, silica-alumina, and zeolites. In contrast to physical adsorption, there are no complete books devoted to this aspect of catalyst characterization however, there is a chapter in Anderson that discusses the subject. 

Alkalis are the most important electropositive promoters of metal and metal oxide catalysts. They are used in many important industrial catalysts but are also quite suitable for fundamental studies since they can be easily introduced under vacuum conditions on well-characterized model metal surfaces. 

Selective oxidation of p-xylene to terephthaldehyde (TPAL) on W-Sb oxide catalysts was studied. While WO3 was active in p-xylene conversion but non-selective for TPAL formation, addition of Sb decreased the activity in p-xylene conversion but increased TPAL selectivity significantly. Structure change was also induced by Sb addition. Evidences from various characterization techniques and theoretical calculation suggest that Sb may exist as various forms, which have different p-xylene adsorption property, reactivity toward p-xylene and TPAL selectivity. Relative population of each species depends on Sb content. 

In this paper, the preparation, characterization and the catalytic performance of the Moo.esVoasWo.ioOx-mixed oxide as a partial oxidation catalyst for the methanol to formaldehyde reaction was studied. 

In Chapter 1 we emphasized that the properties of a heterogeneous catalyst surface are determined by its composition and structure on the atomic scale. Hence, from a fundamental point of view, the ultimate goal of catalyst characterization should be to examine the surface atom by atom under the reaction conditions under which the catalyst operates, i.e. in situ. However, a catalyst often consists of small particles of metal, oxide, or sulfide on a support material. Chemical promoters may have been added to the catalyst to optimize its activity and/or selectivity, and structural promoters may have been incorporated to improve the mechanical properties and stabilize the particles against sintering. As a result, a heterogeneous catalyst can be quite complex. Moreover, the state of the catalytic surface generally depends on the conditions under which it is used. 

In this chapter we have limited ourselves to the most common techniques in catalyst characterization. Of course, there are several other methods available, such as nuclear magnetic resonance (NMR), which is very useful in the study of zeolites, electron spin resonance (ESR) and Raman spectroscopy, which may be of interest for certain oxide catalysts. Also, all of the more generic tools from analytical chemistry, such as elemental analysis, UV-vis spectroscopy, atomic absorption, calorimetry, thermogravimetry, etc. are often used on a routine basis. 

Caris-Veyrat, C. et al., Cleavage products of lycopene produced by in vitro oxidations characterization and mechanisms of formation, J. Agric. Food Chem., 51, 7318, 2003. Caris-Veyrat, C. et al., Mild oxidative cleavage of beta, beta-carotene by dioxygen induced by a ruthenium porphyrin catalyst characterization of products and of some possible intermediates, New J. Chem., 25, 203, 2001. 

In this paper we attempt a preliminary investigation on the feasibility of catalytic combustion of CO/ H2 mixtures over mixed oxide catalysts and a comparison in this respect of perovskite and hexaaluminate type catalysts The catalysts have been characterized and tested in the combustion of CO, H2 and CH4 (as reference fuel). The catalytic tests have been carried out on powder materials and the results have been scaled up by means of a mathematical model of the catalyst section of the Hybrid Combustor. 

Active catalyst sites can consist of a wide variety of species. Major examples are coordination complexes of transition metals, proton acceptors or donors in a solution, and defects at the surface of a metallic, oxidic, or sulphidic catalyst. Chemisorption is one of the most important techniques in catalyst characterization (Overbury et al., 1975 Bartley et al, 1988 Scholten et at, 1985 Van Delft et al, 1985 Weast, 1973 and Bastein et al., 1987), and, as a consequence, it plays an essential role in catalyst design, production and process development. 

Catalyst characterization - Characterization of mixed metal oxides was performed by atomic emission spectroscopy with inductively coupled plasma atomisation (ICP-AES) on a CE Instraments Sorptomatic 1990. NH3-TPD was nsed for the characterization of acid site distribntion. SZ (0.3 g) was heated up to 600°C using He (30 ml min ) to remove adsorbed components. Then, the sample was cooled at room temperatnre and satnrated for 2 h with 100 ml min of 8200 ppm NH3 in He as carrier gas. Snbseqnently, the system was flashed with He at a flowrate of 30 ml min for 2 h. The temperatnre was ramped np to 600°C at a rate of 10°C min. A TCD was used to measure the NH3 desorption profile. Textural properties were established from the N2 adsorption isotherm. Snrface area was calcnlated nsing the BET equation and the pore size was calcnlated nsing the BJH method. The resnlts given in Table 33.4 are in good agreement with varions literature data. 

Busca, G. (1998) Spectroscopic characterization of the acid properties of metal oxide catalysts, Catal. Today, 41, 191. 

Kustov, L.M. (1997) New trends in IR-spectroscopic characterization of acid and basic sites in zeolites and oxide catalysts, Top. Catal., 4, 131. 

Mowery, D.L., Graboski, M.S., Ohno, T.R. et al. (1999) Deactivation of Pd0-Al203 oxidation catalyst in lean-burn natural gas engine exhaust aged catalyst characterization and studies of poisoning by H20 and S02, Appl. Catal. B 21, 157. 

Metalloporphyrinosilicas as a new class of hybrid organic-inorganic materials were prepared by polymerization of 3- er -butyl-5-vinylsalicylaldehyde with styrene and divinylbenzene and used as selective biomimetic oxidation catalyst.27 Synthesis and structural characterization of rare-earth bisfdimethyl-silyl)amides and their surface organometallic chemistry on mesoporous silicate MCM-41 have been reported.28... 

The vanadium(IV) complex of salen in zeolite was found to be an effective catalyst for the room temperature epoxidation of cyclohexene using t-butyl hydroperoxide as oxidant.88 Well-characterized vanadyl bis-bipyridine complexes encapsulated in Y zeolite were used as oxidation catalysts.101 Ligation of manganese ions in zeolites with 1,4,7-triazacyclononanes gives rise to a binu-clear complex stabilized by the zeolites but allows oxidation with excellent selectivity (Scheme 7.4). 

It should be observed that curve C (Fig. 31) which characterizes the steady activity of the catalyst surface may be directly compared to activity curves obtained by other techniques. The evolutions of heat as a function of time produced by the reaction of doses of reaction mixture at the surface of four different nickel oxide catalysts are, for instance, plotted on Fig. 32. These curves are very similar indeed to the kinetic curves obtained with the same catalysts in a classical static reactor (Fig. 33) (8). 

The aim of this study is to develop model reaction for the characterization of the acidity and basicity of various transition aluminas, the experimental conditions being close to that for catalysis use. Among various model reactions, the transformation of cyclopentanol and cyclohexanone mixture was chosen for this work. Indeed, this reaction was well known for estimating simultaneously the acid-base properties of oxide catalysts [1], Two reactions take place the hydrogen transfer (HT) on basic sites and the alcohol dehydration (DEH) on acid sites. The global reaction scheme is shown in Figure 1. 

The forty-eighth volume of Advances in Catalysis includes a description of a new and increasingly well understood class of catalysts (titanosilicates), a review of transmission electron microscopy and related methods applied to catalyst characterization, and summaries of the chemistry and processes of isobutane-alkene alkylation and partial oxidation and C02 reforming of methane to synthesis gas. 

In this book we describe some the most often used techniques in catalyst characterization (see Fig. 1.5). We will highlight those methods that have been particularly useful in the study of metal, oxide and sulfide catalysts, and related model systems. Zeolites and techniques such as nuclear magnetic resonance [2,3,16] fall outside the scope of this book. A number of books on catalyst characterization are listed in the references [3, 16-22],... 

In conclusion, Mossbauer spectroscopy has matured into one of the classical techniques for catalyst characterization, although its application is limited to a relatively small number of elements which exhibit the Mossbauer effect. The technique is used to identify phases, determine oxidation states, and to follow the... 

In catalyst characterization, diffraction patterns are mainly used to identify the crystallographic phases that are present in the catalyst. Figure 6.2 gives an example where XRD readily reveals the phases in an Fe-MnO Fischer-Tropsch catalyst [7], The pattern at the top is that of an MnO reference sample. The diffraction pattern of the reduced Fe-MnO catalyst shows a peak at an angle 29 of 57°, corresponding to metallic iron, and two peaks which are slightly shifted and broadened in comparison with the ones obtained from the bulk MnO reference. The Mossbauer spectrum of the reduced catalyst contains evidence for the presence of Fe2+ ions in a mixed (Fe,Mn)0 oxide [7], and thus it appears justified to attribute the distortion of the XRD peaks to the incorporation of Fe into the MnO lattice. Small particle size is another possible reason why diffraction lines can be broad, as we discuss below. 

The main drawback of the use of UV-Vis spectroscopy for catalyst characterization is that the data commonly show broad and overlapping absorption bands with little chemical specificity. Also, it is often quite difficult to properly interpret the resulting spectra. Lastly, quantitative analysis is only possible at low metal oxide loadings [114],... 

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