Steam Reforming Catalyst Formulation

Giroux et al. and Farrauto et al., from Engelhard, presented a proprietary catalyst formulation for autothermal reforming, whicii was actually composed of a layer of platinum/rhodium steam reforming catalyst covered with a platinum/pallachum partial oxidation catalyst [57,107]. The catalyst was capable of reforming natural gas. 

The complete steam reforming of acetic acid can be achieved over commercial Ni-based catalysts [79]. The operating temperature of these systems is aWays higher than 650 °C. The robustness of the catalysts based on Ni guarantees operation over thousands of hours, but this metal leads to extensive coke formation. In order to improve the stability, La203 vas introduced in the catalyst formulation [258]. 

Other Commercial Catalyst Formulations. Many papers and patents have recently appeared which are also addressed to the problem of maintaining mechanical strength as well as activity and chemical stability during steam reforming and methanation. Hence, only selected examples will be given in the following paragraphs. 

Banks, Paterson, and Williams of British Gas have described951 the preparation and properties of a coprecipitated Ni-Al203 catalyst (50 wt% Ni) to which were added 1.0 wt% of an alkali metal and 0.5 wt% of ruthenium. This material was shown to have desirable properties when used for the steam reforming of a hydrocarbon oil in the temperature range 410-476 °C. It is, however, not very likely that such a catalyst will be used commercially because of the high cost of ruthenium and the limited supplies of this metal which are available. Another British Gas patent, referred to previously, introduces chromium into the formulation to improve the stability of the resultant catalyst.77... 

Steam reforming is the reaction of steam with hydrocarbons to make a manufactured gas containing mostly methane with trace amounts of ethylene, ethane, and hydrogen. For the manufacture of this gas, a representative catalyst composition contains 13 wt % Ni, 12.1 wt % U, and 0.3 wt % K it is particularly resistant to poisoning by sulfur. To make hydrogen, the catalyst contains oxides of Ni, Ca, Si, Al, Mg, and K. Specific formulations are given by Satterfield (1980). 

Figure 2.18. Temperature-programmed reduction profiles of CuZnAlZr oxide catalysts for oxidative steam reforming of methanol. Note that a gradual shift in peak maximum toward lower temperatures, when A1 is substituted by Zr, indicates an improvement in CuO reducibility upon A1 substitution by Zr in the Cu/Zn0-Al203 formulation. Adapted from Velu et al.177...

After a short review of recent process developments, the most important work on the formulation and performance of reforming catalysts, and then on the mechanism and kinetics of hydrocarbon-steam reactions, is described. The reactivity of different hydrocarbons and the reforming of higher boiling point hydrocarbons is considered. The next section deals with carbon formation and finally relevant patents filed since 1973 are briefly described. 

Patent specifications relating to the formulation of catalysts for steam reforming published since 1974 are listed in Table 6. The catalyst composition is indicated and (in parentheses) the name of the assignee company or individual. In each case the numbered specification is the earliest version published later specifications, e.g. British and U.S., if published, can be identified in the Chemical Abstracts Patent Concordance. 

Research on supported Ni catalysts, used for steam reforming and other applications " , has dealt with factors affecting their activity and stability. Catalyst formulation and the extent to which interaction occurs between NiO and the support are important factors influencing the reduction of NiO to Ni in the catalyst and the catalysts subsequent behavior. The influence of the support on the metal is illustrated by NiO on AI2O3 or MgO. It is well known that NiO deposited on oxide supports is less readily reduced than bulk NiO. Furthermore, growth of crystallites of the metal oxide can be retarded by a suitable support. For instance, the presence of MgO retards the growth of NiO. When NiO is calcined at 500°C for 4 h, NiO crystallites increase to about 30 nm, whereas in a NiO/40% MgO solid solution, the crystallites grow to only 8 nm (Fig. 1). ... 

The purpose of the present paper was 10 study the feasibility of using the hydrogenolysis of cyclopentane and the hydrogenation of benzene, typical examples of structure-sensitive and nonstructure-sensitive reactions, to measure the residual activity of specific centers remaining after coke is deposited on supported Ni and Ni-K catalysts. Potassium was chosen as the promoter, for it is often used in the formulation of nickel-based catalyst for steam reforming of naphthas (refs. 2-3). Comparisons between the promoted and unpromoted catalysts were performed at two different extents of metal-support interaction, which were caused by calcination to 400 or 700°C Some attention was paid to changes in selectivity induced by alkali promotion and/or carbon deposition. 

Steam reforming of naphtha is well established in industry. Characteristics of the reactions are summarized including a discussion of possibilities to control carbon formation by catalyst formulation. The progress in tubular reforming of natural gas related mainly to use of higher temperatures can be implemented for liquid feedstocks by installation of an adiabatic prereformer. This is illustrated by industrial examples. 

The mechanism of formation of whisker carbon has been studied over the last 30 years. It is the main route for carbon formation in steam reforming. The understanding of the mechanism has been the basis for design principles for carbon-free operation and for optimum catalyst formulation. Recent work has confirmed the importance of surface steps for carbon formation and given new ideas for promotion of the catalyst by inhibition of full dissociation of methane. 

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