Deactivation and Coke Formation on Nickel−Tungsten Supported on Silica−Alumina Catalysts

Abstract

Nickel−tungsten oxides supported on silica−alumina catalysts were submitted to the coking reaction with n-octane at 150, 250, and 300 °C. The characteristics of deposited coke with different times on stream were studied using the temperature-programmed oxidation (TPO) technique. The results revealed that the strength and density of acid sites as well as the reaction temperature affect the nature of the coke formed: at 300 °C, it was observed that for the WT7 catalyst, the most acidic solid, there were two peaks corresponding to two kinds of coke recorded in TPO profiles, while at 150 °C only one peak was observed. On the other hand, for the WT4 catalyst, the less acidic sample, only the soft coke was observed. In addition, the oxidation temperature of coke shifted to higher values with high medium acid sites concentration and high temperature values with the increase of coke deposits. Besides, coke molecules interacted preferentially with the most acidic sites, which was confirmed by the strong deactivation in the first reaction stages, especially for the WT7 catalyst. For the regeneration tests, the collected data suggested that the coked WT4 catalyst showed a good combustion behavior; it was regenerated at 500 °C for 1 h, whereas the coked WT7 could not be regenerated at this temperature.

Effect of Metal Ratio and Preparation Method on Nickel–Tungsten Carbide Catalyst for Hydrocracking of Distillers Dried Grains with Solubles Corn Oil

“…Also, the catalysts with Ni−W ratios of 1:1 and 2:1 deactivated very fast, which can be attributed to the deposition of coke. 27 However, the catalyst with Ni−W ratio of 9:1 showed the best conversion of corn oil (100% for the first 2 days) and showed a significant resistance against deactivation. Table 3 indicates that the selectivity of diesel was low for every ratio except for the Ni−W ratio of 9:1 (almost 100% for the first 2 days).…”

“…The conversion of corn oil for the first day was high for every Ni–W ratio except for the Ni–W ratio of 1:9. Also, the catalysts with Ni–W ratios of 1:1 and 2:1 deactivated very fast, which can be attributed to the deposition of coke . However, the catalyst with Ni–W ratio of 9:1 showed the best conversion of corn oil (100% for the first 2 days) and showed a significant resistance against deactivation.…”

Facile Biodiesel Synthesis from Esterification of Free Fatty Acids Catalyzed by SO3H-Functionalized Ionic Liquid

“…Therefore, an esterification pretreatment of the free fatty acids to alkyl esters in the presence of an acid catalyst could efficiently eliminate the problems. In this regard, the traditionally used acid catalysts such as sulphuric acid, organic acids and solid acids etc., are usually associated with one of the following disadvantages such as high temperature, long reaction time, high cost and moisture sensitivity of the catalyst, tedious isolation procedures, equipment corrosion and environmental problems 7,8 . In order to abate these deficiencies, several…”