Cyclopentanes hydrogenolysis

The order of metals in their activities is also known for some reactions other than ethane hydrogenolysis. Maurel and Leclercq (220) found the following order for cyclopentane hydrogenolysis Ru > Rh, Ir > Os > Ni > Pt > Pd > Cu, Fe. Various Co catalysts showed activity between that of Os and Pt (most likely the influence of an uncomplete reduction). Carter el at. (221) found the following order for heptane hydrogenolysis Ru > Rh, lr Pt > Pd. The common features of these orders in activities are evident. 

Fig. II. Effect of the hydrogen partial pressure on the rate of cyclopentane hydrogenolysis Pt/AUOj A, sulfurized Pt/ALO,.

Effects are on the rate constant K (molecules hour 1 accessible Pt atoms 1 atmospheres ) and on the ratio of the adsorption equilibrium constants of cyclopentane and hydrogen (cyclopentane hydrogenolysis). 

Catalysts were evaluated by means of different test reactions cyclohexane dehydrogenation, cyclopentane hydrogenolysis and coking reaction with cyclopentane at high pressure (15 bar). The reaction conditions are summarized in Table 1. Before performing the test reactions, presulfided catalysts were reduced at 500°C for 8 h and non-sulfided catalysts for 2 h. Coke... 

Table 2 shows conyersion values obtained during cyclopentane hydrogenolysis on the two series of Pt-Re bimetallic catalysts (Cl Coimpregnation, CR Catalytic reduction). The different catalysts were activated by direct reduction (R) or by calcination followed by reduction (C). 

In the case of catalysts prepared by catalytic reduction (redox technique) the conversion is higher when catalysts were activated by direct reduction than when activation was done using calcination followed by reduction (C). In that last case, activity for cyclopentane hydrogenolysis is comparable to that obtained on R-Re catalysts prepared by coimpregnation. 

For bimetallic catalysts, the sulfur coverage (9s) is lower on catalysts exhibiting the highest Pt-Re interaction determined by cyclopentane hydrogenolysis (Table 2). 

Cyclopentane hydrogenolysis. Catalysts were tested with cyclopentane hydrogenolysis imder the following conditions 0.9 bar hydrogen and 0.1 bar of cyclopentane at 290°C. 

The different catalysts prepared in this study were characterized by their catalytic activities for cyclohexane and cyclopentane hydrogenolysis which, in reaction on platinum, are generally considered to be structure-insensitive and structure-sensitive, respectively. 

Figure 1 Activity for cyclopentane hydrogenolysis. Catalysts A catalytic reduction B coimpregnation, C successive impregnation CR calcined and reduced R only reduced catalyst.

The sextet-doublet model was adapted for 1-5 dehydrocyclization, the reverse of cyclopentane hydrogenolysis, and it was proposed that physically adsorbed alkane reacts with chemisorbed hydrogen according to a push-pull mechanism (772) (Scheme 55). 

Figure 11 (left) Number of carbon atoms, C270> deposited per platinum surface site, Pt j,j., and activity in cyclopentane hydrogenolysis, a, as a function of platinum dispersion. 

The aim of this work is to study the sintering of Rh and PtRh catalysts by means of oxidation and steam reforming activities in propane conversion. Changes in the steam reforming activity have been compared with those obtained in cyclopentane hydrogenolysis, a reaction extremely sensitive to the state of Rh in the catalyst [12]. 

Table 2 Cyclopentan hydrogenolysis activities (pmol C5H10 per pulse per gram at 200°C) on fresh and treated catalysts...

Another useful probe for indicating the extent of Pt-Re alloying on reforming catalysts is cyclopentane hydrogenolysis, the alloy being intrinsically more active than either pure metal [79, 80]. In Fig. 9.3, the synergy in the activity shows a great interaction between the two metals for Pt-Re catalysts prepared by catalytic reduction [30]. 

Fig. 9.3 Cyclopentane hydrogenolysis (1(T mol converted per second and per gram of Pt) on Pt-Re catalysts prepared by catalytic reduction in HNO3 medium ( ) catalysts activated by reduction (hydrogen, 8h, 500°C) ( ) catalysts activated by calcination (air, 4h,...

---