Activation of Supports

Catalytic Activity of Supported Organometallic Compounds in Ethylene... 

Table 3.1 Catalytic activity of supported lb metal catalysts for MeOH oxidation [53]. ...

Abstract This review is a summary of supported metal clusters with nearly molecular properties. These clusters are formed hy adsorption or sirnface-mediated synthesis of metal carbonyl clusters, some of which may he decarhonylated with the metal frame essentially intact. The decarhonylated clusters are bonded to oxide or zeolite supports by metal-oxygen bonds, typically with distances of 2.1-2.2 A they are typically not free of ligands other than the support, and on oxide surfaces they are preferentially bonded at defect sites. The catalytic activities of supported metal clusters incorporating only a few atoms are distinct from those of larger particles that may approximate bulk metals. 

Hutchings, G.J. (1985) Vapor phase hydrochlorination of acetylene Correlation of catalytic activity of supported metal chloride catalysts. Journal of Catalysis, 96, 292-295. 

It was seen when studying mixed systems Pt-WOj/C and Pt-Ti02/C that with increasing percentage of oxide in the substrate mix the working surface area of the platinum crystallites increases, and the catalytic activity for methanol oxidation increases accordingly. With a support of molybdenum oxide on carbon black, the activity of supported platinum catalyst for methanol oxidation comes close to that of the mixed platinum-ruthenium catalyst. 

Electrocatalytic activity of supported metal particles has been investigated on surfaces prepared in an ultrahigh vacuum (UHV) molecular beam epitaxy system (DCA Instruments) modified to allow high throughput (parallel) synthesis of thin-film materials [Guerin and Hayden, 2006]. The system is shown in Fig. 16.1, and consisted of two physical vapor deposition (PVD) chambers, a sputtering chamber, and a surface characterization chamber (CC), all interconnected by a transfer chamber (TC). The entire system was maintained at UHV, with a base pressure of 10 °mbar. Sample access was achieved through a load lock, and samples could be transferred... 

Date M, Okumura M, Tsubota S, Haruta M. 2004. Vital role of moisture in the catalytic activity of supported gold nanopaiticles. Angew Chem Int Ed 43 2129-2132. 

Catalyst Activation Gas phase activation of supported DENs was examined using in-situ FTIR spectroscopy and FTIR spectroscopy of adsorbed CO. For in-situ dendrimer decomposition studies, the spectra were collected under a gas flow composed of 20% 02/He or 20% H2/He. The supported DEN sample was pressed into a self-supporting wafer, loaded into a controlled atmosphere IR cell, and collected as the sample background. The temperature was raised stepwise and spectra were collected at each temperature until little or no change was observed. After oxidation, the sample was reduced in 20% H2/He flow with various time/temperature combinations. The sample was then flushed with He for lhr at the reduction temperature. After cooling under He flow, a background spectrum was collected at room temperature. A 5% CO/He mixture was flowed over the sample for 15 minutes, followed by pure He. IR spectra of CO adsorbed on the catalyst surface were collected after the gas phase CO had been purged from the cell. 

A high metathesis activity was also observed when CH3Re03 was chemisorbed on Nb205. There appears to be a correlation between the catalytic activity and the Lewis acidity of the support.267 Catalytic activity of supported tungsten phenoxide in olefin metathesis was also studied.268... 

Basinska, A., and Domka, F. 1997. The influence of alkali metals on the activity of supported ruthenium catalysts for the water-gas shift reaction. Catal. Lett. 43 59-61. 

In contrast, the activity of supported rhodium catalysts is determined principally by the concentration of accessible surface Rh atoms, which catalyze methane decomposition, followed by CO2 reduction (186). As a result, the support plays a minimal role in the rhodium-containing catalysts. 

T. F. Jaramillo, S. H. Baeck, B. R. Cuenya, and E. W. McFarland, Catalytic activity of supported au nanoparticles deposited from block copolymer micelles, J. Am. Chem. Soc. 125, 7148-7149... 

As shown below, for structure-insensitive reactions the surface characteristics of the single crystal catalysts simulate the activity of supported catalysts in the same reactant environment. This proves to be most fortunate since the advantages of single crystals are retained along with the relevance of the measurements. Moreover, the use of single crystals allows the assessment of the crystallographic dependence of structure-sensitive reactions. 

Table V. Carbonylation Activities of Supported Molybdenum and Nickel-Activated Carbon Catalysts ...

JaramUlo TF, Baeck S-El, Cuenya BR, McFarland EW (2003) Catalytic Activity of Supported Au Nanoparticles Deposited from Block Copolymer Micelles. J Am Chem Soc 125 7148-7149... 

The differences between catalysts treated at 125 and 100 °C suggest that lower activation temperatures might produce catalysts that are more active. This data is collected with different conversions, at different temperatures, and with small masses of catalyst, so observed rates in these experiments are only qualitative activity measures. Variances in surface water content, which might be substantial at these temperatures, also can dramatically affect the activity of supported Au catalysts. (11) Consequently, it is difficult to draw meaningful conclusions regarding catalyst activity from the low temperature activation data. 

If a large excess of phosphine were present, then the mechanism given in reaction (41) would predict a decrease in catalytic activity. In agreement with this, the activity of supported catalysts does decrease as the ratio of f—PPh2 to Rh increases (91). 

The special nature of gold chemistry and gold catalysis is now known and many applications can be based on the low-temperature activity of supported gold compared to that of other metals [196]. 

A second advantage of preparing peptides by sequential acylation of support-bound amines arises from the fact that activated A -acyl amino acids readily form oxa-zolones, which quickly racemize under basic conditions, such as in the presence of excess amine. Hence, carboxyl group activation of support-bound peptides in the presence of an amine will readily lead to racemization (Figure 16.2). 

Activated A-alkoxycarbonyl amino acid derivatives, on the other hand, do not cyclize as readily as A -acyl amino acids, and therefore racemize more slowly. Accordingly, solid-phase peptide synthesis is generally performed by acylation of support-bound amines with activated A -alkoxycarbonyl amino acids. Examples of the preparation of peptides by the inverse strategy (first amino acid linked to the support via its amino group as carbamate activation of support-bound AAacylamino acids) have, nevertheless, been reported [13-16]. 

In this paper the term electronics is used with a different connotation it stands for the description of electron transitions to and from, as well as within supported catalysts. It will be shown that in many cases such transitions are responsible for the enhanced or reduced catalytic activities of supported catalysis. In this concept, supported catalysts are described as solid state systems in which a catalytically active component (the... 

Figure 3.5 Catalytic activity of supported Pd and Au catalysts for CO oxidation. Metal loadings 1.0wt%, D-P method, calcined at 573 K, CO 1.0vol.% in air, SV 20000h 1 mL per g-cat. ...

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