Carbon deactivation of Fischer-Tropsch ruthenium catalyst

Abstract

Carbon deactivation of a 0.5 wt % Ru/7-AI203 surface-impregnated catalyst was studied by using a Berty continuous-stirred, gas-solid reactor (CSGSR)-gas chromatograph setup. The experimental variables were as follows: temperature, 473-573 K; pressure, 2-6 atm; weight hourly space velocity, 0.85, 16.5 h_1; H2/CO feed ratio, 3 and 2; and synthesis time, 0.5-5 h. Carbon deposited in a synthesis run was measured by integrating the methane evolution profile during catalyst reduction at 723 K in H2. Significant amounts of carbon were deposited, increasing to several monolayers during 5-h synthesis periods. The methanation rate decreased as the synthesis continued, while the selectivity for C2-C4 hydrocarbons showed a maximum during the initial stages of deactivation. The kinetic data could be correlated by assuming both hydrogen-assisted CO dissociation and hydrogenation of surface carbon to be rate determining. The turnover numbers for methanation (NCHf) and carbon deposition (A/C/FJ are given by eq 3 and 4.

The effect of CO on CO2 methanation over Ru/Al2O3 catalysts: a combined steady-state reactivity and transient DRIFT spectroscopy study

“…They showed that the deactivation rate increases with the CO partial pressure, due to an inhibition of CO on H 2 adsorption. Similar effects were also observed by other authors [40,59], although the reason for deactivation was not clearly explained. Bell et al [60] proposed that carbon deposition was the main reason for the catalyst deactivation, while Gupta et al [61] proposed that the formation of di-and tri-carbonyls, more difficult to hydrogenate, is responsible for the deactivation during CO hydrogenation.…”

“…Furthermore, Ru-based catalysts are less prone to deactivation than the other methanation catalysts [10], even though some deactivation has been reported in the literature when working with gas feeds containing CO [36]. Sintering of small Ru-particles [37,38] and formation of volatile species as Ru-carbonyls [39] are reported among the possible causes of deactivation, although the most critical deactivation mechanism seems to be the formation and deposition of carbonaceous species, leading to active site blocking [40]. Carbon deposition is strongly affected by the process conditions [41,42] but does not lead to permanent deactivation, since high temperature treatments in hydrogen can restore the initial activity [43,44].…”

CO Poisoning of Ru Catalysts in CO2 Hydrogenation under Thermal and Plasma Conditions: A Combined Kinetic and Diffuse Reflectance Infrared Fourier Transform Spectroscopy–Mass Spectrometry Study

“…36 Since the adsorption energy of CO (−2.3 eV) is much lower than that of CO 2 (−0.52 eV), 37 preferential adsorption of CO and inhibited CO 2 adsorption on the Ru surface are expected and, thus, a decrease in CO 2 conversion. It was proposed that the formation of strongly adsorbed carbonyl species 11,38 due to the presence of CO might be the dominant factor for catalyst deactivation. Therefore, the mechanism of CO poisoning of the Ru/SiO 2 catalyst was investigated by in situ DRIFTS analysis (to be discussed later).…”

Support effects on the structure and performance of ruthenium catalysts for the Fischer–Tropsch synthesis

“…It is also proposed that the surface carbon species formed by hydrogen-assisted CO dissociation participate in the FT synthesis reaction and as precursor for the species that causes catalyst deactivation. 11,71,72 Recent theoretical studies suggest, however, that the CO dissociation ability is favored on couples of atoms on monoatomic steps being the key requirement for Ru to develop a good FTS catalyst, 73,74 followed by hydrogenation and coupling of CH x fragments 75 or CO insertion. 74 Experimental studies have shown that water presents a positive effect on the reaction rate and selectivity, in part due to its ability to remove surface carbon atoms, 4 and in part because Ru particles around 8 nm perform better than smaller particles for FTS.…”