Catalytic reforming combined catalyst systems

One such catalytic system has been pilot planted by Toyo Engineering Company (7 ). It utilizes a combination catalyst and specially designed feedstock vaporization system to process hydrocarbons as heavy as crude oil to obtain reasonable conversions to hydrogen and carbon monoxide. Another process announced by Grand Paroise uses a fluidized bed of catalyst for the reforming step (8). Heat required is introduced into the fluidized catalyst by burning fuel inside of tubes immersed in the bed. Both of these systems have been extensively tested in large pilot installations and could be included in commerical installations in the near future if justified by economic considerations. 

Numerous other bimetallic situations may occur in catalysis, perhaps related to the addition of alkali cations. For example, Burch (3) has examined cases where Group 4A species such as Sn are added to the Pt/Cl/Al203 reforming combination in order to enhance the stability, and also favorably affect related features. Sexton et al. (7) have examined similar systems with ESCA, and, as noted above, have found that in the common catalytic doping range, e.g., Pt(0.25-0.75 wt%) and Sn(0.4-0.75 wt%), they were able to monitor the behavior of the tin and found that in the oxidized version Sn(+4) species were present, whereas, following reduction, surface Sn(+2) entities persisted (7). We have also examined simulated Pt/Sn catalysts of similar composition and found that reduction yields Sn(II). This was consistent with the arguments of Burch (3), and seemed to be contrary to the alloy formation concept of Sachtler et al. (4b) and Clarke (4a). 

The studies reviewed here focus on Sn/Pt because of the opportunity afforded by the ordered alloys formed in this system for improving our basic understanding, as well as the commercial importance of Pt-Sn catalysts in naphtha reforming and their potential for other selective hydrogenation and dehydrogenation reactions. These studies combined detailed structural characterization of the alloy surfaces with UHV studies of adsorption and reaction of hydrocarbons and other small molecules, and measurements of the rate and selectivity of catalytic reactions at atmospheric pressure over these model catalysts. 

The alloy catalysts used in these early studies were low surface area materials, commonly metal powders or films. The surface areas, for example, were two orders of magnitude lower than that of platinum in a commercial reforming catalyst. Hence these alloys were not of interest as practical catalysts. The systems emphasized in these studies were combinations of metallic elements that formed continuous series of solid solutions, such as nickel-copper and palladium-gold. The use of such systems presumably made it possible to vary the electronic structure of a metal crystal in a known and convenient manner, and thereby to determine its influence on catalytic activity. Bimetallic combinations of elements exhibiting limited miscibility in the bulk were not of interest. Aspects of bimetallic catalysts other than questions related to the influence of bulk electronic structure received little attention in these studies. 

A prototype for a methanol reforming silicon reactor was designed at Lehigh University [11,12,31]. Their microreaction system, made of silicon wafers, consisted of four main components a mixer/vaporizer of methanol and water, a catalytic steam reformer with a copper catalyst, the combined water gas shift reactor-membrane (as mentioned before) and integrated resistive heaters, sensors and control electronics. The reformer was tested with a stainless-steel housing. The authors reported a conversion of 90% for methanol, which corresponds to a power output of 15 W. 

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