Ethane Steam Reforming over a Platinum/Alumina Catalyst: Effect of Sulfur Poisoning

Abstract

In this study we have examined the adsorption of hydrogen sulfide and methanethiol over platinum catalysts and examined the effect of these poisons on the steam reforming of ethane. Adsorption of hydrogen sulfide was measured at 293 and 873 K. At 873 K the adsorbed state of hydrogen sulfide in the presence of hydrogen was SH rather than S, even though the Pt:S ratio was unity. The effect of 11.2 ppm hydrogen sulfide or methanethiol on the steam reforming of ethane was studied at 873 K and 20 barg. Both poisons deactivated the catalyst over a number of hours, but methanethiol was found to be more deleterious, reducing the conversion by almost an order of magnitude, possibly due to the co-deposition of sulfur and carbon. Changes in the selectivity revealed that the effect of sulfur was not uniform on the reactions occurring, with the production of methane reduced proportionally more than the other products, due to the surface sensitivity of the hydrogenolysis and methanation reactions. The water-gas shift reaction was affected to a lesser extent. No regeneration was observed when hydrogen sulfide was removed from the feedstream in agreement with adsorption studies. A slight regeneration was observed when methanethiol was removed from the feed, but this was believed to be due to the removal of carbon rather than sulfur. The overall effect of sulfur poisoning was to reduce activity and enhance hydrogen selectivity.

Adsorption of hydrogen sulphide over rhodium/silica and rhodium/alumina at 293 and 873 K, with co-adsorption of carbon monoxide and hydrogen

“…0:4 S ads ð Þþ0:6 HS ads ð Þþ0:7 H 2 Therefore, over Rh/silica, the primary adsorbed state is HS(ads), which is not the case for Rh/alumina, where the H 2 :S ratio is 1:1 indicating that the only adsorbed state is S(ads) (Tables 1, 2). This is different from the Pt/alumina and Pt/silica systems where both catalysts had a H 2 :S ratio of *0.7:1 [8], indicating that dissociation is enhanced over Rh/alumina.…”

“…Over Rh/alumina, a S:Rh ratio of *1:1 is obtained, which is higher than that observed with the silica catalyst. This is the opposite of what is found with carbon monoxide adsorption and hydrogen sulphide adsorption over Pt/alumina, where the alumina-supported catalyst gave a lower ratio [8]. The greater than 1:1 CO:Rh ratio was expected over the alumina supported catalyst, as it is known that the gem-dicarbonyl Rh I (CO) 2 species can be formed leading to a greater than 1:1 ratio.…”

“…This suggests the formation of the bulk sulphide, Rh 2 S 3 . When hydrogen was cofed with hydrogen sulphide at 873 K (Table 4), the amount of sulphur adsorbed decreased significantly (S:Rh * 1:1) and the degree of dissociation also decreased, but not by as much as found with platinum catalysts, where the H 2-:S(ads) ratio decreased from 1:1 to 0.44 for Pt/alumina and 0.25 for Pt/silica [8]. This is to be expected, as we are now displacing the following equilibria to the left-hand side:…”

“…This work follows on from a study over Pt/alumina and Pt/ silica where the adsorption of hydrogen sulphide was examined in relation to its effect on steam reforming [8]. In this study, the adsorption of hydrogen sulphide and methanethiol over Rh/silica and Rh/alumina at 293 K will be examined and the amount compared with that found from carbon monoxide chemisorption.…”

Effective hydrogen productions from propane steam reforming over spinel-structured metal-manganese oxide redox couple catalysts

“…Steam reforming of hydrocarbons involves a highly endothermic reaction; thus, noble metal catalysts such as Pt, Ru, and Rh, have been used to promote the reaction in previous studies. However, their high cost has been a barrier to their commercial utility; hence, research has recently moved toward using cheaper transition metal catalysts.…”