Platinum zeolites

F. Ribeiro, C. Marcilly, and M. Guisnet, Hydroisomerization of n-hexane on platinum zeolites. I. Kinetic study of the reaction on platinum/Y-zeolite catalysts influence of the platinum content, J. Catal., 78, 261-21A (1982). 

Catalytic Destruction of Volatile Organic Compounds on Platinum/Zeolite... 

A. Renouprez, R. Stockmeyer, C.J. Wright (1979). J. Chem. Soc. Faraday Trans. I, 75,2473-80. Diffusion of chemisorbed hydrogen in a platinum-zeolite. 

Bernard. J.R. Platinum-zeolite interactions in alkaline L zeolites (correlations between catalytic activity and platinum state). . Chem. Soc.. Faradaq-Trans., 1 1981. 77. 49. 

F1 NMR of chemisorbed hydrogen can also be used for the study of alloys. For example, in mixed Pt-Pd nanoparticles in NaY zeolite comparaison of the results of hydrogen chemisorption and F1 NMR with the formation energy of the alloy indicates that the alloy with platinum concentration of 40% has the most stable metal-metal bonds. The highest stability of the particles and a lowest reactivity of the metal surface are due to a strong alloying effect. 

Direct hydroxylation of benzene to phenol could be achieved using zeolite catalysts containing rhodium, platinum, palladium, or irridium. The oxidizing agent is nitrous oxide, which is unavoidable a byproduct from the oxidation of KA oil (see KA oil, this chapter) to adipic acid using nitric acid as the oxidant. 

Surface science studies have generated much insight into how hydrocarbons react on the surfaces of platinum single crystals. We refer to Somorjai [G.A. Somor-jai. Introduction to Surface Chemistry and Catalysis (1994), Wiley, New York] for a detailed overview. Also, the reactions of hydrocarbons on acidic sites of alumina or on zeolites have been studied in great detail [H. van Bekkum, E.M. Flanigan and J.C. Jansen (Eds.), Introduction to Zeolite Science and Practice (1991), Elsevier, Amsterdam],... 

While the discovery of the catalytic properties of zeolites was driven by the desire to improve industrial prcKessing, the development of emission control catalysts was necessitated by governmental fiat. The first requirement was for 90+% removal of CO and of hydrocarbons, a goal which could not be met by oxidation with base metal oxides. To achieve the required spedfications during automobile operations, it was necessary to develop supported platinum catalysts. Originally the support was alumina in pellet form. Later platinum on cordierite was used in honeycomb form, containing 200-400 square channels per square inch. 

Zeolites, clays, and platinum metal catalysis. This area is reviewed in detail by Barr (1990), and here again problems of specimen charging may arise. 

Burch, R., Breen, J.P. and Meunier, F.C. (2002) A review of the selective reduction of NO, with hydrocarbons under lean-burn conditions with non-zeolitic oxides and platinum group metal catalysts, Appl. Catal. B, 39, 283. 

The NH4-Y (CBV712, ao = 24.35 A), H-Beta (CP811E-75), NH4-Beta (CP814E) zeolites were obtained from Zeolyst International. The NH4-Y and Beta zeolites were transformed to proton forms through step calcination procedure in a muffle oven. Zeolites containing 1 wt-% platinum were prepared by wet-impregnation method using hexachloroplatinic acid as the Pt-source. 

The changes in the product concentrations are more pronounced in case of Pt-zeolites. Particularly the rate of decalin isomerization is considerably enhanced by the addition of platinum. The ratio of Iso/ROP decreases from the value of 12 after 1 h to the value of 1.4 after 9 h. The ratio of ROP/CP decreases from the values close to 3 within the first 3 h to the value of 1.3 after 9 h. This is in contrast to H-Beta-25, where the ratio ROP/CP is almost constant during the entire experiment and its values do not exceed 1.5. The same trends are... 

This is a quite remarkable result, as the chemoselective hydrogenation of geraniol over a heterogeneous catalyst has rarely been reported. It can be carried out over platinum containing zeolite (9), over Pt/Al203 modified with carboxylic acids (10), over Ni/diatomaceous earth and alkali hydroxides or carbonates (11) or NiRaney and alkali or alkaline earth metal hydroxides (12), yields never exceeding 85%. 

Pt/H-MCM-22 catalysts for methane combustion have been prepared by ion-exchange of a highly crystalline H-MCM-22 zeolite using [Pt(NH3)4](N03)2. The activation procedure of the catalyst precursor has been optimized and all steps monitored by HRTEM, SEM and FTIR of CO adsorbed. The preliminary decomposition/calcination of the ion exchanged sample is very crucial in that influence the final properties of platinum active species. 

Keywords platinum, MCM-22 zeolite, IR spectroscopy, HRTEM, CO adsorption. 

The synthesis procedure led to a highly crystalline MCM-22 zeolite, as indicated by XRD data (Fig. 1A, a). The introduction of platinum by ion exchange procedure does not modify the crystallinity of the zeolite (Fig. 1A, b). SEM micrographs show that the sample obtained in static hydrothermal conditions is characterized by the presence of homogeneous round-shaped particles of ca. 10 pm in diameter formed by aggregation of lamellar particles [7,8], The morphology of the zeolite is not modified after platinum introduction (Fig. IB). 

The transformation of n-hexadecane was carried out in a fixed-bed reactor at 220°C under a 30 bar total pressure on bifunctional Pt-exchanged HBEA catalysts differing only by the zeolite crystallites size. The activities of the catalysts and especially the reaction scheme depended strongly on the crystallites size. Monobranched isomers were the only primary reaction products formed with the smallest crystallites, while cracking was the main reaction observed with the biggest crystallites. This was explained in terms of number of zeolite acidic sites encountered by the olefinic intermediates between two platinum particles. 

Keywords hydroisomerization, n-hexadecane, platinum, HBEA zeolite, crystallite size... 

All the catalysts contained 1 wt.% platinum, introduced into the zeolite through ion exchange by [Pt(NH3)4)]2+ in competition with NH4+ (NH4+/Pt=100), followed by calcination under dry air flow at 450°C for 4h. The dispersion of platinum, measured using CO adsorption followed by infrared spectroscopy, was about 60%. Whatever the crystallite size, the catalysts were first pelletized, then crushed and sieved to obtain 0.2 - 0.4 mm particles. 

The method of metal introduction should significantly affect the degree of proximity between the Pt and acidic sites, hence the catalytic properties. In a previous study, the behavior of Pt/MCM-22 samples in n-hexane transformation was explored by Martins et al. [11]. In this study the same reaction was used in order to evaluate the influence of the mode of Pt introduction. Three 1 wt.% Pt/MCM-22 samples were prepared, differing by the mode of platinum introduction ion exchange, incipient wetness impregnation or mechanical mixture of the zeolite with Pt/Al203. 

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