Support effect

For Pd supported on the monolithic samples, Rokosz et showed two major forms of phosphorus compounds, alumina phosphate within the washcoat and zinc, calcium and magnesium phosphates in an overlayer. The contaminants 

Liu and Park in their study on deactivated automotive catalysts in the presence of zinc dialkyl dithiophosphate (ZDDP) and Pb showed the formation of AIPO4 by reaction wit the support. The deactivation was due to several types of interaction with the alumina support, including the formation of an impervious layer on the washcoat or sintering of the y-alumina particles in the washcoat. 

We will now briefly discuss all the different effects, first those that affect the intrinsic hydrogen sorption properties of the active phase deposited on the support 

Gold nanoclusters on gallia polymorphs have also been proven to be versatile green catalysts for the oxidative esterification of several alcohols [88, 89]. Early work by 

Mesoporous aluminas are hypothesized as efficient supports in terms of catalysis for anchoring metal nanoparticles. They offer higher stabihty and dispersion of the nanoparticles apart from facilitating easy diffusion of reactants and product 

Hydroxyapatite (CajQ(P04)g(0H)2) has also attracted considerable interest as a catalyst support. In these materials, wherein Ca sites are surrounded by P04 tetrahedra, the introduction of transition metal cations such as Pd into the apatite framework can generate stable monomeric phosphate complexes that are efficient for aerobic selox catalysis [99]. Carbon-derived supports have also been utihzed for this chemistry, and are particularly interesting because of the ease of precious metal recovery from spent catalysts simply by combustion of the support. Carbon nanotubes (CNTs) have received considerable attention in this latter regard because of their superior gas adsorption capacity. Palladium nanoparticles anchored on multiwalled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) show better selectivity and activity for aerobic selox of benzyl and cinnamyl alcohols [100, 101] compared to activated carbon. Interestingly, Pd supported on MWCNTs showed higher selectivity toward benzaldehyde, whereas activated carbon was found to be a better support in cinnamyl alcohol oxidation. Functionalized polyethylene glycol (PEG) has also been employed successfully as a water-soluble, low-cost, recoverable, non-toxic, and non-volatile support with which to anchor nanoparticulate Pd for selox catalysis of benzyl/cinnamyl alcohols and 2-octanol [102-104]. 

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This section discusses the company culture that is necessary to support effective data collection and root cause analysis. 

An explanation was suggested for these solvent and support effects and this is represented in Fig. 19. Thus, in solvents with greater dielectric permittivity, e, the cationic complex is situated further from the clay surface and the stereoselectivities are therefore more similar to those obtained in homogeneous phase. On the other hand, in solvents with low e, close ion pairs are formed and the surface has a larger effect on the reaction. 

It is concluded from these results that with this kind of non-C2 symmetric ligand (that led necessarily to poor enantioselectivities in homogeneous phase), it is possible to exploit support effects to change the trans/cis selectivity and to improve the enantioselectivity. This is demonstrated for the trans-cyclopropanes obtained with ligand 10a in styrene. Due to the relative disposition of the ester and phenyl groups in the transition state, support ef-... 

In the case of the reaction between N-acryloyloxazolidin-2-one and cy-clopentadiene, both catalysts showed activities and enantioselectivities similar to those observed in homogeneous phase. However, a reversal of the major endo enantiomer obtained with the immobilized 6a-Cu(OTf)2 catalyst, with regard to the homogeneous phase reaction, was noted. Although this support effect on the enantioselectivity remains unexplained, it resembles the surface effect on enantioselectivity of cyclopropanation reaction with clay supports [58]. 

Chemisorption on nonmetallic catedysts should provide the number of catal3rtic sites and for comparative purposes a single Mg can be taken as a catalytic site on metals. This permits the calculation of turnover frequencies which was a new concept in post ICC 1 and which permitted intercomparison of catalyst activities. For the first time then, one has been able, for example, quantitatively to discuss support effects in Rh/support catalysts. 

Except for support effects, structure sensitivity has usually appeared in one of two aspects, variation of rate with svirface crystal face or with particle size. In ICC 1 Gwathmey reported in one of the first experiments with single crystal faces that different faces machined fi om Ni single crystal spheres catalyzed the hydrogenation of ethylene at different rates (ICC 1 paper 5). 

From the previous results, it has been proven that the nature of the support, although it has no significant influence on the Pd electronic properties, modifies the catalytic properties of the solids To permit a better understanding of these supports effects, the surface properties of the supports (in the presence of the metal) have been studied, in particular the acidic properties and the oxygen mobilities. The A1203 and Z1O2 supports have been mainly onsidered. 

Supports effects do not drastically modify Pd this is shown by XPS and by IR spectroscopy of adsorbed CO Nevertheless, the catalytic performances of the materials have been significantly improved with the supports containing zirconia. For instance, the activity of Pd/Al203-Ba0-Zr02 nearly reaches the activity of the Pt-Rh/Al203 reference. 

Poisoning of deNOx catalysts by SO2 could also be a problem since diesel fuels contain small amounts of sulfur compounds. Only a few studies deal with this subject [11-13]. It appears from the literature that for Cu catalysts the use of MFI as a support reduces the inhibition by SO2. Support effects also appear in the case of Co since Co/MFI is much less sensitive to SO2 than Co/ferrierite [13]. Since this support effect may be related to acidity, it becomes important, to investigate the influence of SO2 on the properties of Cu catalysts supported on Si02, AI2O3, MFI, BEA and unpromoted or sulfate promot Ti02 and Zr02- These latter have been reported active for deNOx [14]. 

The comparison of the results of TPR with those of NO TPD on Cu on silica and alumina suggests that a better dispersion of the Cu species induces a higher reducibility of Cu, as reported elsewhere [16]. On the other hand, a strong support effect appears in the case of Cu supported on zirconia or titania, which shows the easiest reducibility in spite of a low dispersion as judged from XRD. 

In addition, it sustains CO electro-oxidation at relatively low overpotential, and there are crystal face dependences for both the ORR and CO oxidation. Since Au is also a system that exhibits both particle size and support effects in heterogeneous catalysis, it provides an interesting model system for smdying such effects in electrocatalysis. 

Support effects in electiocatalysis, 567-586 Surface diffusion, 163, 173-177 Surface Enhanced Infrared Reflection Adsorption Spectroscopy (SEIRAS), 183... 

Except Ru (not usable in TWC because of the volatility of its oxide [68]), the most active metal is the rhodium. This has been largely confirmed by further studies so that Rh may be considered as a key-component of TWC for NO reduction [69,70], As far as Pd is concerned, it seems that the active site is composed of Pd"+ —Pd° pairs, which may explain the higher activity of Pd in N0+C0+02 mixture (T5( 200°C) [71]. A detailed kinetic study by Pande and Bell on Rh catalysts has evidenced a significant support effect [72], The kinetic data were represented by a conventional power law expression ... 

Dhainaut, F., Pietrzyk, S. and Granger, P. (2007) Kinetics of the NO + H2 reaction over supported noble metal based catalysts Support effect on their adsorption properties, Appl. Catal. B 70, 100. 

Because the size regime of n=l-6 atoms is of great practical significance to the spectroscopic, chemical and catalytic properties of supported metal clusters in both weakly and strongly interacting environments (28), it is important to study very small metal clusters in various types of substrate as well as in the gas phase. In this way, one can hope to develop a scale of metal cluster-support effects (guest-host interactions) and evaluate the role that they play in diverse technological phenomena. 

Iglesia, E., Soled, S.L., and Fiato, R.A. 1992. Fischer-Tropsch synthesis on cobalt and ruthenium. Metal dispersion and support effects on reaction rate and selectivity. J. Catal. 137 212-24. 

Duprez and coworkers—support effect on WGS rate/180-160 switching method to quantify surface O diffusion and role of metal as porthole for exchange/ relationship of formate and carbonate surface mobility to O mobility during WGS. 

Imamura, Kaito, and coworkers—metal-support effects observed after calcination. Imamura et al 9X reported a strong metal-support interaction between Rh and Ce02, whereby high surface area ceria calcined at low temperature (550 °C) was able to transport Rh particles to the bulk, as measured by XPS. They suggested that despite the low degree of exposure of the Rh particle at the surface, the exposed Rh was highly active for the methanol decomposition reaction. 

A piecewise linear turnover approximation supports effective and accurate decision making on sales turnover based on price-quantity functions and elasticity as an alternative to exact quadratic optimization. 

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