Catalyst Preparation Techniques Research Articles

Si-MCM41 Supported Sulfated Zirconia and Nafion for Ether Production

Various unsupported and supported sulfated zirconia and Nafion catalysts were prepared and investigated for etherification of C6 olefins with methanol. Supported sulfated zirconia and Nafion generally show higher activity than unsupported sulfated zirconia and Nafion. The nature of the support and catalyst preparation techniques were found to affect the catalytic activity. Mesoporous Si-MCM41 with high surface area was the best support for the acid catalysts. Si-MCM41 supported sulfated zirconia and Nafion catalysts produced higher ether yields than other supports and in some cases exhibited a better catalytic activity than the reference resin catalyst, Amberlyst 15. The wt % loading of acidic component and reaction temperature were important factors influencing the catalytic behavior.

Carbon-Supported Copper Catalysts: II. Crotonaldehyde Hydrogenation

The adsorption and catalytic behavior of Cu supported on different forms of carbons, i.e., activated carbon, graphitized carbon fibers, and diamond powder, were examined during crotonaldehyde hydrogenation. Activities as well as turnover frequencies (TOFs) varied significantly as a function of the support, the pretreatment temperature, and the catalyst preparation technique; for example, activities at 423 K ranged from 0.23 to 18 μmol/s/g cat while TOFs ranged from 0.001 to 0.13 s−1 after reduction at 573 K. A maximum in TOF was exhibited by each catalyst as a function the fraction of Cu0 at the surface, i.e., Cu0/(Cu0+Cu+1), which is attributed to enhanced reactivity of crotonaldehyde adsorbed on Cu+1 sites. Whereas typical Cu catalysts, including Cu powder, exhibited similar TOF values after a given reduction step, significantly higher TOFs were obtained with Cu dispersed on a nitric acid-treated activated carbon; this is attributed to additional adsorption sites on the carbon surface for crotonaldehyde which allow it to react with hydrogen spilled over from Cu0 sites. In contrast, unusually low TOFs and a higher selectivity to crotyl alcohol were exhibited by Cu deposited on the graphitized fibers by an ion-exchange technique, which may be due to small Cu particles preferentially stabilized along the edges of the graphitic basal planes. Selectivity to crotyl alcohol was routinely near zero after 3 h on stream. Both diffuse reflectance FTIR spectroscopy (DRIFTS) and kinetic data obtained during crotyl alcohol and butyraldehyde hydrogenation indicated stronger adsorption and higher reactivity of crotyl alcohol on Cu, presumably leading to these low steady-state selectivities. DRIFT spectra taken under reaction conditions revealed adsorbed crotonaldehyde, provided evidence for a monohydrogenated reactive intermediate with detectable surface coverage, and detected no adsorbed butyraldehyde. A Langmuir–Hinshelwood model incorporating this reaction intermediate gave an excellent fit of the kinetic data and provided physically meaningful values for enthalpies and entropies of adsorption.

Commercial polypropylene catalysts

The continuing commercial success of polypropylene (PP) is attributed to the versatility and favorable economics of this polymeric hydrocarbon. Of key importance to this success is the catalytic system employed for PP production, and particularly the combination of catalyst performance and properties of PP obtained. The gradual improvement of the commercial PP catalyst during the last 35 years has led the way for new developments in manufacturing processes and marketed products. At this stage of development, Ti-Mg chloride-based supported catalysts are the most attractive for commercial application. These catalysts realize substantially superior activity and product ash content, relative to the older mechanically or chemically activated TiCl 3 catalysts. Controlled particle morphology supported catalysts with very high activity and high stereospecificity and PP powder bulk density are employed in all PP manufacturing processes, i.e., gas-phase, bulk, and slurry. Performance improvements beyond those realized with the currently commercial catalysts, attained by advanced catalyst preparation and activation techniques, will further increase plant capacities, improve economics, and expand product slate by allowing production of specialty homo- and copolymer products.

Selective chemisorption and oxidation/reduction kinetics of supported copper oxide catalysts prepared from copper(II) acetylacetonate

Copper(II) oxide catalysts, prepared by non-aqueous adsorption of Cu(acac) 2 on Cab-O-Sil followed by thermal decomposition, were titrated by NO and N 20 to characterize the dispersion of the copper ions. These catalysts showed molar ratios of NO/Cu close to unity when the Cu loadings were less than 2.5 wt%. For samples having loadings greater than 3.8 wt% Cu, the NO/Cu molar ratios were near 0.7. The NO/Cu molar ratio also depended upon the catalyst preparation technique subsequent to the initial impregnation with Cu(acac) 2 when the Cu loadings were ≥ 3.5 wt%. Samples washed with fresh acetonitrile showed NO/Cu ratios close to unity, whereas, those not so washed showed NO/Cu ratios near 0.7. IR spectra of NO sorbed on partially decomposed samples showed only “bent” CuNO, whereas, NO sorbed to the sample which was totally decomposed showed both linear and bent CuNO. Selected samples (3.8 and 8.6 wt% Cu) were reacted with N 2O to determine the dispersion of the Cu. The sample having 8.6 wt% Cu reacted with the N 2O to give a dispersion of 0.43; whereas the other sample (3.8 wt%) did not react with the N 2O. This dispersion determined by N 2O agreed with that calculated from NO titration (0.47) if the NO/Cu stoichiometry was assumed equal to unity. Subsequently, these catalysts were reduced in H 2 and reoxidized in O 2 to determine the oxidation and reduction kinetics as a function of copper loading. The 3.8 wt% Cu sample lost 1 O/Cu upon reduction in H 2 and gained l O/Cu for reoxidation in O 2 for up to five redox cycles; whereas, the 8.6 wt% Cu sample showed a stoichiometry of O/Cu which decreased from 1.00 to 0.57 after five redox cycles.

FTIR studies of catalyst preparation effects on spatial propagation of oscillations during CO oxidation on [formula omitted

In situ selected-area FTIR spectroscopy and localized catalyst temperature measurement techniques have been utilized to show that the oscillatory behavior of a Pt SiO 2 catalyst during CO oxidation is related to the spatial distribution of crystallites. Various catalyst preparation techniques have been used to prepare catalysts with different crystallite sizes and different separations among the crystallites, these catalysts being characterized by chemisorption and optical microscopy. It is shown that the occurrence of oscillations is affected by the crystallite size distribution and by the separation among crystallites. The results are explained in terms of a model which relates the separation and size distribution of crystallites to the spatial propagation of oscillatory states.

The microstructure of bimetallic [formula omitted] catalysts: A chemisorption and analytical electron microscopy study

Supported bimetallic RuCu SiO 2 catalysts are characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, electron microdiffraction, and chemisorption. Metal particles up to 4 nm in diameter are bimetallic, while particles larger than 4 nm contain only Cu. Considerable compositional nonuniformity is observed from one individual metal particle to the next. Microdiffraction patterns obtained from individual particles can be attributed to either Ru or Cu suggesting no significant modification in crystallographic structure of either metal component. Addition of Cu to Ru results in a drastic suppression of H 2 chemisorption while the extent of O 2 chemisorption is not as strongly affected. The suppressed H 2 chemisorption capability of Ru in the bimetallic catalysts is an indication of atomic interdispersion of Ru and Cu on the surface of the bimetallic clusters, leading to the break-up of the Ru ensembles which would be necessary for dissociation of molecular hydrogen. The influence of catalyst preparation techniques on the relative interdispersion of Ru and Cu and consequent discrepancies in the RuCu literature are discussed.

Development and commercialization of new FCC catalysts.

The characteristics and commercial results of newly developed FCC catalysts named are described. MRZ catalysts consist of three types: high liquid yield, high octane and high metal tolerance series. The general characteristics of MRZs are as follows: 1) low coke and gas formations, 2) high hydrothermal stability, and 3) low catalyst consumption. The commercialization of the new catalysts was attained to apply new catalyst preparation technique and to use highly silicious Y zeolite as an active ingredient. The low coke forming characteristics of MRZ catalysts are attributed to unique pore structure and acidity of its matrix. The high hydrothermal stability of MRZs is attributed to low surface area of matrix and the application of high SiO2/Al2O3 mole ratio of Y zeolite. The commercial application of MRZ catalysts for FCC plants showed good performances and high metal tolerance. It is, therefore, expected that these are good catalysts for heavy oil cracking.