Mark G. White

Supported catalysts prepared from mononuclear copper complexes: Catalytic properties

Abstract Model surfaces of copper on silica (Cab-O-Sil) were prepared and characterized by four probe reactions: methyl acetate hydrogenolysis, ethanol and methanol decomposition, and acetaldehyde hydrogenation. The model catalysts were prepared by thermal decomposition of copper acetylacetonate {Cu(acac) 2 } deposited on silica either as a monolayer or as multiple layers. The prior characterizations suggested that thermal decomposition of monolayer films of Cu(acac) 2 produced isolated copper species which could be oxidized and reduced up to 10 times without changing the dispersion of the copper. Thermolysis of the multiple layers of Cu(acac) 2 produced a copper surface of lower dispersions (ca. 70%) which decreased to 30% after only five oxidation/reduction cycles. These two surfaces were appropriate models to study the catalysis of oxygenates over Cu ensembles.

Uses of polynuclear metal complexes to develop designed dispersions of supported metal oxides

Abstract The new generation of catalysts will be designed according to the traditional methods of scientific pursuit using the relationships of catalytic properties to surface structure. However, new methods of catalyst synthesis are necessary to usher in this new generation of catalysts. We believe that one possible route to this catalyst synthesis will begin by fabricating the catalytic ensemble as a discrete metal complex in a single crystal which will allow for its structure to be known by diffraction methods. This crystal will be solvated into discrete metal complexes which are attached to the appropriate ceramic support as a single layer of such replicates. In the ideal synthesis, the catalytic ensemble will require no further treatment to render it active and the structure of the ensemble on the ceramic is the same as its structure in the single crystal. For these materials, the relationships between structure and properties are unambiguous and the dream of creating heterogeneous catalysts with homogeneous properties becomes a reality. Unfortunately, the synthesis of active metal complexes may be limited to very small number. In these cases when no active metal complex may be synthesized, alternative preparations may require further treatment to render active the metal complexes. Such active catalysts may be developed after thermolysis of the supported metal complexes to form a “designed dispersion” of the metal oxides.

The effect of water on the structure of supported vanadium oxide structures: an FT-RAMAN, in situ DRIFT and in situ UV-VIS diffuse reflectance study

A promising way to create supported metal oxide catalysts consists of the irreversible adsorption and subsequent thermolysis of metal acetylacetonate complexes. Spectroscopic techniques are often used in the evaluation and assessment of the final catalytic surface structure. In this paper, the use of FT-RAMAN, in situ UV-VIS diffuse reflectance DRS and in situ diffuse reflectance infrared spectroscopy is discussed in the evaluation of silica supported VOx structures. It is argued that water drastically influences the surface structure of these catalysts. Its effects are noticeable in the stages of pretreatment of the support, the actual synthesis and in the post-synthesis storage of the catalyst

The Uses of Polynuclear Metal Complexes to Develop Designed Dispersions of Supported Metal Oxides: Part I. Synthesis and Characterization

One way to design a catalyst begins with a consideration of thereaction mechanism to the desired product so that only the chemistryrequired of that mechanism will be present on the surface. The reactionmechanism will suggest the structure(s) to be developed on the surface whichshould be stabilized against changes during operation. We believe that thisideal may be approached by decorating surfaces or porous powders with amonolayer of metal complexes having the desired structures. These complexesmay be partially decomposed to develop a high dispersion of the supportedmetal oxide.

Recent advances in nanocatalysis research

Recent developments in nanocatalysis research are reviewed. They demonstrate the important role of nanocatalysts in the advances of catalytic sciences and technology. Special emphasis is given to the synthesis and characterization of nanosized, supported metal and metal oxide structures.

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 N20 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 N2O to determine the dispersion of the Cu. The sample having 8.6 wt% Cu reacted with the N2O to give a dispersion of 0.43; whereas the other sample (3.8 wt%) did not react with the N2O. This dispersion determined by N2O 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 H2 and reoxidized in O2 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 H2 and gained l O/Cu for reoxidation in O2 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.

Polynuclear metal complexes as model mixed oxide catalysts: An ion exchange support interaction

The authors have reported on the preparation and characterization of supported polynuclear metal complexes containing two types of metal ions (Cu/sup 2 +/ and M/sup 3 +/ where M = Al, Cr, or Fe). These +3 complexes were balanced by three ClO/sub 4//sup -/ in the unsupported single crystal state. The authors showed that the strong ammonia sorption stoichiometry to each cluster depends upon the metal ion, M/sup 3 +/; however, the sorption stoichiometry/cluster did not change when the cluster loading on Cab-O-Sil was increased from 10 to 30 wt%. They speculated the cluster interacted strongly with the Cab-O-Sil support to form a monolayer covering. In this note the authors report their studies of the cluster-support interaction. The cluster-support interactions were studied by X-ray diffraction of the supported catalysts at different loadings and quantitative analysis for counterion concentrations, ClO/sub 4//sup -/, at each loading. 8 references.

Polynuclear metal complexes as model mixed oxide catalysts: Selective chemisorption of ammonia and nitric oxide

Abstract Model mixed oxide catalysts were prepared by supporting polynuclear metal (M 3+ and Cu 2+ ) complexes of the form M[(μ-OH)Cu(μ-OCH 2 CH 2 NR 2 )] 3+ 6 (M = Al, Cr, and Fe) on Cab-O-Sil (28 wt% loading). The supported complexes exhibited both Bronsted (bridging OH groups) and Lewis (Cu 2+ ions) acidities. While the coordinatively saturated central M 3+ ion was not an available Lewis site, changing M 3+ influenced catalyst acidity through an apparent ligand effect. Reported are acidity characterizations by ammonia adsorption, first with Cu 2+ ions open to estimate overall acidity, and second with Cu 2+ ions blocked to evaluate the Bronsted acidity. Selective sorption of nitric oxide was an effective Lewis site poison at temperatures to 80 °C. Ammonia sorption to unpoisoned supported complexes revealed increasing overall acidity for the series Al to Cr to Fe (with NH 3 adsorption heats of 4.6, 8.1, and 8.2 kcal/mol, respectively). Ammonia sorption to NO-poisoned supported complexes indicated increasing Bronsted acidity with NH 3 adsorption heats of 2.6, 8.5, and 8.2 kcal/mol, respectively.

Polynuclear metal complexes as model mixed oxide catalysts

Abstract Selective chemisorptions of CO and NH 3 were used to describe the sorption properties of polynuclear metal complexes of Cu 2+ and M 3+ ( M = Al, Cr, and Fe) supported on silicon dioxide (Cab-O-Sil). On those samples heated to less than 180 °C no IR spectrum of CO could be detected; thus, indicating all the Cu ions were cupric and the ferric, chromic ions were coordinately saturated. IR spectra of chemisorbed NH 3 showed relaxations at frequencies characteristic of Lewis-bound (3350-3280 cm -1 ) and protonic-bound (3210-3175 cm -1 ) NH 3 for all clusters having open cupric sites. The Lewis-bound NH 3 IR peaks disappeared when the Cu 2+ sites were sterically blocked whereas the relaxations of NH 3 bound to other sites (3210-3175 cm -1 ) did not. The 54 °C isotherm of the strongly bound NH 3 showed an average site density that increased from 2.2 to 3.0 sites/cluster with M = Al, Cr, and Fe. For an Fe complex with all the Cu 2+ sites sterically blocked the NH 3 site density was 1.8 sites/cluster. The activation energy for desorbing NH 3 from the 32 wt% samples changed with M 3+ : 11.9, 14.8, 16.0 kcal/mol for Al, Cr, and Fe, respectively. Desorption of NH 3 from the 10 wt% samples corrected for NH 3 bound to the exposed Cab-O-Sil showed E d = 11.9, 19.8, and 21.8 kcal/mole. The E d for the Lewis-bound NH 3 to the Cu 2+ was only 32 kcal/ mole and that for the NH 3 bound to other sites was 17.6 kcal/mole for the Fe-Cu/Cab-O-Sil (10 Wt%).

Direct liquid‐phase side‐chain oxidation of alkylbenzenes over 2 catalyst

Only the side‐chain oxidation of alkylbenzenes (R–C6H3–R′–R″ R=H, Me, Et, Pri R′=H, Me; and R″=H, Me) by oxygen (35–50 atm, 200)C° is promoted in the presence of [Pd(phen)(OAc)2].