Platinum reactions over supported

Fig. 33. The reaction path obtained with pure benzene initial composition for the reaction over supported platinum catalyst at 399°C., 20 atm of hydrogen and 5 atm of hydrocarbon.

Table 12 Specific activities for the CO/H2 reaction over supported platinum ...

Reactor System. A general purpose reactor system shown in Figure 1 was used in this work to study catalytic oxidation reactions over supported platinum catalyst pellets. This equipment allowed up to six precise gas mixtures to be prepared and made available for feed to the reactor. The switching valve directed a desired gas mixture flow to the reactor while another gas mixture flow was precisely measured by the bubble flow meter. 

Hanson FV, Boudart M. 1978. The reaction between H2 and O2 over supported platinum catalysts. J Catal 53 56-67. 

When one considers the various results from the reactions of labeled and unlabeled hexanes over supported catalysts and over thick and ultra-thin films, the conclusion emerges that catalysts with very small platinum particles (ultrathin films or 0.2% platinum/alumina) strongly favor reactions via an adsorbed C5 cyclic intermediate, but at large particle size... 

Bond rupture probabilities have also been reported by Myers and Munns (160) for hydrogenolysis reactions over a number of supported catalysts containing platinum in the range 0.1-1%. The reactions were carried out in the region of 350°-480°C. Provided one confines the comparison to nonacidic supports, these results are in tolerable agreement with the data in Table XI. 

Hydrogen peroxide is commercially produced by autooxidation of ethyl anthraquinol in a solvent such as toluene or ethylbenzene. The product ethyl anthraquinone is reduced by hydrogen over supported nickel or platinum catalyst to regenerate hack the starting material, ethyl anthraquinol for a continuous production of H2O2. The reaction steps are ... 

Noncarbonium-ion-type 1-2-methyl shifts have been described by Barron et al. (11), and by Anderson and Avery (34). The reaction proceeds through a-y-diasorbed intermediates over platinum on neutral supports and does not involve carbonium-ion intermediates. According to this mechanism, the n-butylbenzene isobutylbenzene reaction involves the following steps (surface sites are represented by ) ... 

Now possibilities of the MC simulation allow to consider complex surface processes that include various stages with adsorption and desorption, surface reaction and diffusion, surface reconstruction, and new phase formation, etc. Such investigations become today as natural analysis of the experimental studying. The following papers [282-285] can be referred to as corresponding examples. Authors consider the application of the lattice models to the analysis of oscillatory and autowave processes in the reaction of carbon monoxide oxidation over platinum and palladium surfaces, the turbulent and stripes wave patterns caused by limited COads diffusion during CO oxidation over Pd(110) surface, catalytic processes over supported nanoparticles as well as crystallization during catalytic processes. 

Dynamic reactor studies are not new, but they have not been widely used in spite of the fact that they can provide a wealth of information regarding reaction mechanisms. In this research, oxidation of carbon monoxide over supported cobalt oxide (C03O4) was studied by both dynamic and conventional steady state methods. Among metal oxides, cobalt oxide is known to be one of the most active catalysts for CO and hydrocarbon oxidation, its activity being comparable to that of noble metals such as palladium or platinum. 

Gasolines contain a small amount of sulfur which is emitted with the exhaust gas mainly as sulfur dioxide. On passing through the catalyst, the sulfur dioxide in exhaust gas is partially converted to sulfur trioxide which may react with the water vapor to form sulfuric acid (1,2) or with the support oxide to form aluminum sulfate and cerium sulfate (3-6). However, sulfur storage can also occur by the direct interaction of SO2 with both alumina and ceria (4,7). Studies of the oxidation of SO2 over supported noble metal catalysts indicate that Pt catalytically oxidizes more SO2 to SO3 than Rh (8,9) and that this reaction diminishes with increasing Rh content for Pt-Rh catalysts (10). Moreover, it was shown that heating platinum and rhodium catalysts in a SO2 and O2 mixture produces sulfate on the metals (11). 

Cutlip, M. B., and C. N. Kenney, Limit cycle phenomena during catalytic oxidation reactions over a supported platinum catalyst, ACS Symp. Sen, 65, 475-486 (1978). 

In Table 1 the results are shown for the reaction over a variety of catalysts under a hydrogen atmosphere. It is clear that platinum-supported H-ZSM-5 (Pt-ZS.M-5) or hybrid catalyst containing Pt/Si02 (Pt/Si02 + H-ZSM-5) shows high n-pentane conversion and iso-pentane selectivity while both H-ZSM-5 or Pt/Si02 shows quite low activity and low iso-pentane selectivity. 

The selective production of methanol and of ethanol by carbon monoxide hydrogenation involving pyrolysed rhodium carbonyl clusters supported on basic or amphoteric oxides, respectively, has been discussed. The nature of the support clearly plays the major role in influencing the ratio of oxygenated products to hydrocarbon products, whereas the nuclearity and charge of the starting rhodium cluster compound are of minor importance. Ichikawa has now extended this work to a study of (CO 4- Hj) reactions in the presence of alkenes and to reactions over catalysts derived from platinum and iridium clusters. Rhodium, bimetallic Rh-Co, and cobalt carbonyl clusters supported on zinc oxide and other basic oxides are active catalysts for the hydro-formylation of ethene and propene at one atm and 90-180°C. Various rhodium carbonyl cluster precursors have been used catalytic activities at about 160vary in the order Rh4(CO)i2 > Rh6(CO)ig > [Rh7(CO)i6] >... 

Otto et al. at the Ford Motor Company have published two papers ° on the reaction of NO with NH3 over supported platinum at 200—250 °C in a recirculating reactor. Working at total pressures of about lOOTorr they were able to show that the overall stoicheiometry was virtually independent of NH3/NO ratio and temperature. The approximate product distribution was given by... 

Hudgins 17) has used a sinusoidally varying input in concentration to analyze the frequency response of a reactor for the catalytic dehydrogenation of ethanol using a conventional tubular reactor. Leder and Butt 18) have successfully used frequency response to analyze the dynamic behavior of a fixed-bed catalytic reactor used for the hydrogen-oxygen reaction over a supported platinum catalyst. Hydrogen inlet concentration was varied sinusoidally over frequencies from 2 cycles/ hour to 120 cycles/hour. 

One such alternative system comprises platinum-group metals supported on metal oxides. A number of groups have recently reported that such materials are active for NOx reduction under strongly oxidising conditions [4-6]. However, none of these studies have addressed the fimdamental questions pertaining to the mechanism of the selective reduction of NO on such catalysts, or to the nature of the catalytically active surface. In this paper, we describe the main features of the lean NOx reaction over a series of Pt/Al203 catalysts. We also present an extensive study of the mechanism of this reaction over Pt-based catalysts. 

Irrespective of the nature of the reaction intermediate, enolic type (11) or surface carbide (12), the dechne of the turnover number for the zeolites with higher Si/Al ratio can be explained as follows. For platinum (13) and palladium (14,15) loaded zeolites, support effects are known to exist. The higher the acidity (and the oxidizing power) of the zeolite, the higher will be the electron-deficient character of the supported metal. It also is well established now (16) that the average acidity of hydrogen zeohtes increases with the Si/Al ratio. This explains why the electron deficient character of ruthenium should increase with the Si/Al ratio of the zeolite, and a stronger interaction with adsorbed CO should be expected. Vannice (19,20) reported that the N value for CH4 formation decreases when the heat of adsorption for CO increases. All this explains why the tmnover number of the methanation reaction over ruthenium decreases when the Si/Al ratio of the zeolite support increases. 

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