Coking on nickel catalysts for steam reforming of hydrocarbons

Abstract

Abstract Formation of coke from hydrocarbons at conditions for steam reforming was studied in a thermogravimetric system. A number of catalysts were investigated at 500 °C to elucidate which properties of the catalyst may be important for eliminating coking. The study was supplemented by decoking experiments and examination of samples of catalysts exposed to coking under industrial conditions. The formation of coke at 500 °C was not accompanied by poisoning of the nickel surface as reported for lower temperatures. At temperatures below 650 °C, coking was observed neither on the support nor on a catalyst exposed to total poisoning by sulfur. Coking on some support materials was studied at 750 °C. Formation of coke may be depressed by enhanced steam adsorption on the catalyst. This may be achieved by the presence of alkali or by the use of magnesiabased catalysts, the preparation method being important for the function of the latter catalyst type. The activity for the reforming reaction may influence the coking rate. The results are evaluated on the basis of a simple sequence proposed earlier, and some implications for the operation of tubular reformers are discussed.