PtRe catalyst

Catalysts. Some commercial PtRe catalysts listed in Table I were used in this study as well as some PtSn catalysts on which were reported elsewhere (7). The fresh catalysts B-6, B-7 and B-8 made in China are white because they are unreduced. Catalyst 803 made by Engelhard Corp. was grey because it had been reduced by the manufacturer. 

In the preparation of faujasite zeolite-supported Pt-Re catalysts, bimetallic PtRe clusters have been reported to be predominantly formed when a carbonyl rhenium precursor (Re2(CO)io) is contacted with zeolite in which platinum has been previously introduced and reduced. The preexisting Pt clusters may act as nucleation sites. After reduction, these Pt-Re systems show a high selectivity to CH4 in the hydrogenolysis of n-heptane [58]. 

As shown in Table VI, relatively few bimetallic catalysts have been studied by XAES methods. Yermakov et al. (313) were the first to take up the study of the Re oxidation state in reduced impregnated Re/Al203 and PtRe/Al203 catalysts by means of XAES techniques. It was concluded from edge shifts (0.3 eV shift of the Re Lm absorption maximum per unitary change in... 

The recent accomplishments of near-edge X-ray absorption spectroscopy in catalysis studies are already quite impressive, in particular if one considers the limited availability of suitable X-ray spectrometers. Developments of catalytic interest have concerned the Shell Higher Olefin process, size effects, metal-support interaction, mono- and bimetallic catalysts (in particular the PtRe/Al203 system), the reactivity of supported metal catalysts, dynamical and in situ catalyst studies, and a variety of oxide and sulfide catalysts. Other catalytic problems are now coming within easy experimental reach, such as the study of sulfur poisoning and the nature of coking. 

There is now a consensus that an interaction between Pt and Re is responsible for the catalytic performance of reforming catalysts to quote the words of an inventor in the field — we have to conclude that some interaction between Pt and Re is responsible for the characteristic performance of PtRe . 7... 

In the following, examples of the ensemble control by means of adsorbed poisons are discussed with the the emphasis on steam reforming of methane on sulfur passivated nickel catalysts. The conclusions for ensemble control will be compared with data for catalytic reforming on PtRe(S) catalysts and for the impact of chlorine on partial oxidation of methane on Pd-catalysts. 

TABLE 13.16. Hydrogenolysis of Propane (72 = S2) and of -Butane (Kinetic and Selectivity Parameters) on Pt/Al203 and PtRe/Al203 Catalysts at 603... 

Somewhat different conclusions have been reached in a study of n-butane hydrogenolysis on a series of PtRe/a-AhOs catalyst covering the whole composition range. There was an astronomic factor (x 10 ) between the rates shown by platinum and the Pt25Re7s catalyst (Figure 13.25), and as little as 12.5% rhenium was sufficient to increase methane selectivity and to move the Arrhenius... 

Figure 13.23. Compensation plot of Arrhenius parameters for hydrogenolysis of propane (O) and of n-butane ( ) on Pt/Al203 (EUROPT-3) and PtRe/Al203 (EUROPT-4). The two sets of results (ref. 43, filled points ref. 3, open points) are from independent studies on different batches of catalyst, published respectively in 1989 and 1996.

---