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The discussion is devoted to some controversial points related to the aromatization of paraffins at high temperature (around 500°C), and low hydrogen pressure (1–8 bar) over non-acidic catalysts, in particular platinum plus a second component on a neutral(ized) support. Special attention is paid to those points which relate to the question why the second component enhances the stability of the dehydrocyclization (DHC) activity of supported platinum. We first consider the valence state of the second component. On the basis of, among other factors, the total hydrogen uptake we argue that at least part of the second component is present in the reduced state, while TPR points to alloy formation. A comparison of the catalytic and chemisorptive behaviour of bulk alloys with that of supported bimetallics indicates that modification (alloying) of the gas phase-exposed platinum surface is an essential action of the second component. This, in turn, suggests that the superior stability of bimetallic DHC catalysts is related to the catalytic properties of the alloys. Considering the changes in selectivity observed upon alloying we will argue that the most important one is the enhanced selectivity towards dehydrogenation of paraffins (olefins) to the corresponding olefins (poly-olefins), which leads to the question: “Are bimetallics under DHC conditions merely selective dehydrogenation catalysts?” From the invariance in TON for dehydrogenation per surface-exposed platinum atom up to very high dilution of platinum in gold (< 1% at Pt in Au), we infer that only one platinum atom is involved in the rate-determining step. We will extrapolate the aforementioned results to actual DHC catalysts and consider the proposition that the active site in PtSn, PtRe (S), Pt (S) and deactivated Pt (i.e. Pt (C)) DHC catalysts consists of one platinum atom embedded in an “inactive” matrix. Finally we will list some points deserving further study, amongst them the interpretation of the results of techniques such as TPR, the relative importance of different DHC pathways, the chemisorptive properties of alloys and the causes underlying the low hydrogen uptake of “overreduced” supported platinum catalysts.

THERMODYNAMIC ARGUMENTS TOGETHER WITH THE SOLUTIONS OF SOME DIFFUSION EQUATIONS LEAD TO THE THEORY THAT ONE OF THE CAUSES OF BLISTERING OF BITUMINOUS COATINGS IS THE VARIATION IN GAS PRESSURE. THIS THEORY HAS BEEN CONFIRMED BY SOME EXPERIMENTS. A MODEL IS DISCUSSED THAT GIVES A QUANTITATIVE DESCRIPTION OF THE BLISTERING. LABORATORY RESULTS ARE DISCUSSED IN VIEW OF THE MODEL PREDICTIONS. A PROCEDURE IS PROPOSED TO EXTRAPOLATE THE EXPERIMENTAL RESULTS UNDER LABORATORY CONDITIONS TO PRACTICAL CONDITIONS. /TRRL/