Origins of the poisoning effect of chlorine on the CO hydrogenation activity of alumina-supported cobalt monitored by operando FT-IR spectroscopy

CO Hydrogenation on Cobalt‐Based Catalysts: Tin Poisoning Unravels CO in Hollow Sites as a Main Surface Intermediate

“…Ty pical operando DRIFTS spectra recorded over aperiod of 18 ha re shown in the Supporting Information, Figure S2 for the Sn-free catalyst and are similar to those described in details elsewhere. [11,23] In brief,the bands at about 3000-2800 and below 1650 cm À1 are essentially related to hydrocarbon waxes and formates/CO 2 adsorbed on the support, respectively.T he bands of main interest to this study are adsorbed on metallic cobalt:on-top (linearly) at 2031 cm À1 and bridged/ multi-bonded species below 2000 cm À1 .The intensity of these bands was essentially constant after 3h,e xcept for those associated with waxes that continued growing with time.…”

“…[9] Our recent quantitative IR studies have shown that formates located near to the alumina-cobalt interface could potentially be the sole precursors of methanol, while not those of methane and propene,w hich were the main reaction products. [10] The present contribution will now quantitatively investigate the role of adsorbed CO present over alumina-supported cobalt catalysts.We recently reported that the most active cobalt sites were possibly those associated with the formation of bridged/ multi-bonded CO,w hich are thought to be located at the particle edges or steps.This conclusion was reached by noting that the poisoning of cobalt by chloride affected more the IR band intensity associated with this bridge/multi-bonded CO than that of linear (that is,o n-top) CO. [11] In 1980, Fujimoto and his group suggested for the first time that bridged carbonyls could be active intermediate during CO hydrogenation over Ru and Rh catalysts. [12] On both catalysts,b ridged CO were hydrogenated (mainly to methane) at al ower temperature than that needed to hydrogenate linear CO.S everal other groups proposed that bridged CO formed over cobalt-based catalysts could be involved in the catalytic activity, [13][14][15][16][17][18][19][20][21][22] yet no quantitative structure-activity relationship has yet been reported to the best of our knowledge.We report herein aq uantitative operando diffuse reflectance FTIR spectroscopy (DRIFTS) study in which the hydrogenation of CO is monitored on Sn-modified Co/Al 2 O 3 catalysts under differential reaction conditions.D RIFTS enables monitoring the state of the cobalt surface,i n particular the various adsorbed CO species formed under reaction conditions.…”

“…[3] The nature of the reaction mechanism of the Fischer-Tropsch synthesis is still amatter of debate,aswell as the nature of the active sites. [10] The present contribution will now quantitatively investigate the role of adsorbed CO present over alumina-supported cobalt catalysts.We recently reported that the most active cobalt sites were possibly those associated with the formation of bridged/ multi-bonded CO,w hich are thought to be located at the particle edges or steps.This conclusion was reached by noting that the poisoning of cobalt by chloride affected more the IR band intensity associated with this bridge/multi-bonded CO than that of linear (that is,o n-top) CO. [11] In 1980, Fujimoto and his group suggested for the first time that bridged carbonyls could be active intermediate during CO hydrogenation over Ru and Rh catalysts. [9] Our recent quantitative IR studies have shown that formates located near to the alumina-cobalt interface could potentially be the sole precursors of methanol, while not those of methane and propene,w hich were the main reaction products.…”

“…We recently reported that the most active cobalt sites were possibly those associated with the formation of bridged/ multi-bonded CO,w hich are thought to be located at the particle edges or steps.This conclusion was reached by noting that the poisoning of cobalt by chloride affected more the IR band intensity associated with this bridge/multi-bonded CO than that of linear (that is,o n-top) CO. [11] In 1980, Fujimoto and his group suggested for the first time that bridged carbonyls could be active intermediate during CO hydrogenation over Ru and Rh catalysts. [12] On both catalysts,b ridged CO were hydrogenated (mainly to methane) at al ower temperature than that needed to hydrogenate linear CO.S everal other groups proposed that bridged CO formed over cobalt-based catalysts could be involved in the catalytic activity, [13][14][15][16][17][18][19][20][21][22] yet no quantitative structure-activity relationship has yet been reported to the best of our knowledge.…”

CO Hydrogenation on Cobalt‐Based Catalysts: Tin Poisoning Unravels CO in Hollow Sites as a Main Surface Intermediate

“…We recently reported that the most active cobalt sites were possibly those associated with the formation of bridged/multi‐bonded CO, which are thought to be located at the particle edges or steps. This conclusion was reached by noting that the poisoning of cobalt by chloride affected more the IR band intensity associated with this bridge/multi‐bonded CO than that of linear (that is, on‐top) CO …”