Catalytic behavior

Many investigators have also measured the trace metal content of asphalts (68). The catalytic behavior of vanadium has prompted studies of the relation between vanadium content and an asphalt s sensitivity to oxidation (viscosity ratio). The significance of metals in the behavior of asphalts is not yet well understood or defined. 

The literature on catalytic hydrogenation is very extensive, and it is tempting to think that after all this effort there must now exist some sort of cosmic concept that would allow one to select an appropriate catalyst from fundamentals or from detailed knowledge of catalyst functioning. For the synthetic chemist, this approach to catalyst selection bears little fruit. A more reliable, quick, and useful approach to catalyst selection is to treat the catalyst simply as if it were an organic reagent showing characteristic properties in its catalytic behavior toward each functionality. For this purpose, the catalyst is considered to be only the primary catalytic metal present. Support and... 

The activity, coke, and gas factors are the tests that reflect the relative catalytic behavior of the catalyst. 

A short survey of information on formation, structure, and some properties of palladium and nickel hydrides (including the alloys with group IB metals) is necessary before proceeding to the discussion of the catalytic behavior of these hydrides in various reactions of hydrogen on their surface. Knowledge of these metal-hydrogen systems is certainly helpful in the appreciation, whether the effective catalyst studied is a hydride rather than a metal, and in consequence is to be treated in a different way in a discussion of its catalytic activity. 

The above account of the changes that take place when palladium, nickel, or their alloys are converted into their respective hydrides is of course not an exhaustive survey. Such was not the aim of this section. The conditions under which the hydrides can form and exist and some data on their structure have been presented here only in the detail necessary for further discussion of their role in the catalytic behavior of palladium and nickel. 

However, the experimental evidence collected during recent years, concerning mostly the nickel-copper alloy systems, complicated this almost currently accepted interpretation of the alloy catalytic behavior (45). Chemisorptive and subsequent catalytic phenomena appeared to require a different approach for elucidation. The surface reactivity had to be treated as a localized quality of the atoms at the interface, influenced by their neighbors in the crystal lattice (78-80). A detailed general discussion of catalysis on alloys is beyond the scope of this review. In the monograph by Anderson (81) and in the review by Moss and Whalley (82), recently published, a broad survey of the catalytic reactivity of alloys may be found. 

Sulfided bimetallic clusters which mimic the metal composition of commercial hydrodesulfurization (HDS) catalysts have been prepared and their homogeneous catalytic behavior studied. Reaction of thiophenol with [Mo2Co2(/z4-S)... 

A 5% CoOj/Ti02 catalyst is quite active for the wet TCE oxidation at very low reaction temperatures, such as 310 K, and our proposed model of different forms of CoO species existing with the fresh catalyst can reasonably explain the unsteady-state catalytic behavior at the initial period during the wet catalysis. 

Correlation Between Spectroscopic Measurements and Catalytic Behavior of Selective Oxidation Catalysts... 

Catalytic Behavior and Phase Composition of Bismuth-Iron Molybdates... 

However, we have found that reaction induced restructuring of Bi2FeMo20]2 produces a narked enhancement in catalytic behavior (Table II . X-ray diffraction, in-situ Raman spectroscopy, and photoelectron spectroscopy reveal that the restructuring produces a multiphase system consisting of unreacted Bi FeMo20.2, in combination with Bi2MOj0.2, 0-FeHoO and a small amount of Bi2MoO. The key features of the Raman spectra of the activated catalyst are summarized in Table III. 

Although much progress has been made toward understanding the nature and probable catalytic behavior of active sites on CoMo/alumlna catalysts, much obviously remains to be accomplished. Detailed explanation of the acidic character of the reduced metal sites evidently most important In HDS, and presumably In related reactions, must await the Increased understanding which should come from studies of simplified model catalysts using advanced surface science techniques. Further progress of an Immediately useful nature seems possible from additional Infrared study of the variations produced In the exposed metal sites as a result of variations In preparation, pretreatment, and reaction conditions. 

The surface transformations of propylene, allyl alcohol and acrylic acid in the presence or absence of NHs over V-antimonate catalysts were studied by IR spectroscopy. The results show the existence of various possible pathways of surface transformation in the mechanism of propane ammoxidation, depending on the reaction condition and the surface coverage with chemisorbed NH3. A surface reaction network is proposed and used to explain the catalytic behavior observed in flow reactor conditions. 

The Pd-based catalysts were prepared by wet impregnation of the support with Pd(C5H702)2 dissolved in toluene. After drying at 373 K, the acetylacetonate was decomposed under O2 up to 773 K (0.5 K/min) The catalytic behavior of these solids was compared to that of a reference Pt-Rh/Al203 solid. Some characteristics of the solids are reported in Table 1. 

Effects of Li content on the catalytic behaviors and structures of LiNiLaOx catalysts The dpendence of performance of LiNiLaOx catalysts on Li content at 1073K was shown in Fig.l. When D/Ni mole ratio was 0, the relatively acidic LaNiOx had the highest CH4 conversion(92.0%), but no C2 yielded. The products were CO, CO2 and H2, and CO selectivity was 98.3%. It is not an OCM catalyst but a good catalyst for partial oxidation of methane(POM). With Li content and the baric property of LiNiLaOx catalysts increasing, CH4 conversion and CO selectivity decreased, but there was still no C2 formed imtil Li/Ni mole ratio was 0.4. There was a tumpoint of catalytic behavior between 0.2 and 0.4 (Li/Ni mole... 

In two recent papers [8,10], we have initiated studies aimed at understanding the catalytic behavior of WZ and PtWZ. Our observations, which motivated the present study, can be summarized as follows, a) Water of reduction results in the formation of Br0nsted acid sites, as monitored by pulsed addition of pyridine to a DRIFTS chamber at room temperature [8,10]. In this paper, we have complemented those results with similar pyridine adsorption experiments at... 

To better understand the differences in their catalytic behavior, the catalysts were characterized by XRD and UV-vis DRS. Unfortunately, except for the peak at 77.6° 26 (311 diffraction), the other Au diffraction peaks overlapped with those of y-Al203. The size of the coherent domains of Au, listed in Table I, were estimated using the width of this diffraction peak and the Debye-Sherrer equation. They showed that catalysts of both groups A and C had small coherent domains, whereas those of group B had large domains. 

Hybrid density functional calculations have been carried out for AU-O2, Au-CO, Aui3, AU13-O2, Au -CO, AU13-H2, and AU55 clusters to discuss the catalytic behavior of Au clusters with different sizes and structures for CO oxidation [179]. From these calculations, it was found that O2 and CO could adsorb onto several Au model systems. Especially, icosahedral Aun cluster has a relatively weak interaction with O2 while both icosahedral and cubooctahedral Aui3 clusters have interactions with CO. These findings suggest that the surfaces of the Au clusters are the active sites for the catalytic reactions on the supported and unsupported Au catalysts. 

Before investigating the effect of size, shape, and structure on catalytic behavior, that is, TOFs, a set of five requirements concerning the metal particles has to be met. Besides a monodisperse size distribution, the nanoparticles should be fully reduced, unpoisoned, unperturbed by... 

Catalytic behavior of the synthesized material is superior in comparison with a traditional hydrogenation catalyst which is a powdered Lindlar catalyst (5%Pd-3.5%Pb/CaC03), as can be seen from Figure 9(a) and (b). 

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