Some characteristics of deposits on a commercially aged, gas-oil hydrotreating catalyst

Polymerization of gaseous benzyl alcohol. 2. Kinetic study of the polymerization and of the deactivation for a silica/alumina catalyst

“…The general characteristics of the deactivation by coke deposition were studied before in alcohol dehydration reactions on Si02/Al203 catalysts (Bilbao et al, 1985). The coke is not a well-defined compound but a material that is developing toward high condensation degrees, and it is interpreted that the intermediate compounds as well as the final carbonaceous product occupy acidic sites and contribute to catalyst deactivation (Wukasch and Rase, 1982).…”

Effect of Precipitating Some of the More Intractable Material from a Hydrogen-Donor Solvent Coal Extract Solution on Its Hydroprocessing Behavior

“…Loss of activity can result from coverage of active sites by coke and by trace metals, increased diffusional restrictions due to pore filling or blocking by the deposition of coke and trace metals, and poisoning of active sites by the reversible and irreversible adsorption of heterocyclic compounds, thereby reducing the number of active catalytic sites. [14][15][16][17] Contaminants can also cause decreases in the effective diffusivities of the catalysts. 18 It has been shown that carbonaceous deposits can deactivate the catalyst by uniform poisoning, whereas contaminant metals deactivate the catalyst by shell progressive poisoning.…”

“…Carbonaceous material builds up very rapidly at the start of a coal liquefaction run, with attendant catalyst deactivation. − The accumulation of contaminant metals occurs more slowly than the build-up of carbonaceous material and is responsible for a continued decline in activity after the carbon content has attained a relatively constant value. Loss of activity can result from coverage of active sites by coke and by trace metals, increased diffusional restrictions due to pore filling or blocking by the deposition of coke and trace metals, and poisoning of active sites by the reversible and irreversible adsorption of heterocyclic compounds, thereby reducing the number of active catalytic sites. − Contaminants can also cause decreases in the effective diffusivities of the catalysts . It has been shown that carbonaceous deposits can deactivate the catalyst by uniform poisoning, whereas contaminant metals deactivate the catalyst by shell progressive poisoning. , Changes in catalyst structure, such as losses of active metal or promoter surface areas due to sintering, are usually caused by prolonged exposure to high temperatures.…”

Studies of catalyst samples from a two-stage direct coal liquefaction run

“…Coverage of active sites and pore-mouth blockage can also yield decreased effective diffusivities (Prasher et al, 1978). Coverage of active sites and poremouth blockage occur due to the rapid buildup of carbonaceous deposits and the accumulation of contaminant metals (Ocampo et Tamm et al, 1981; Wukasch and Rase, 1982). It has been shown that carbonaceous deposits can deactivate the catalyst by uniform poisoning, whereas contaminant metals deactivate the catalyst by shell-progressive poisoning (Stephens and Stohl, 1984).…”