Evidence of Structure Sensitivity in the Fischer–Tropsch Reaction on Model Cobalt Nanoparticles by Time‐Resolved Chemical Transient Kinetics

Abstract

The Fischer-Tropsch process, or the catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks. The observed size dependence of cobalt (Co) catalysts for the Fischer-Tropsch reaction was studied with colloidally prepared Co nanoparticles and a chemical transient kinetics reactor capable of measurements under non-steady-state conditions. Co nanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H /CO=2. Large differences in carbon coverage (Θ ) were observed for the two catalysts: the 4.3 nm Co catalyst has a Θ less than one while the 9.5 nm Co catalyst supports a Θ greater than two. The monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles, and the major CO dissociation site is identified as the B -B geometry. The difference in activity of Co nanoparticles was found to be a result of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes.

Mechanism of Cobalt-Catalyzed CO Hydrogenation: 1. Methanation

“…More recently, Ralston et al explained cobalt particle size-dependent CTKA data in terms of structure sensitivity, i.e., lack of B 5 –B sites for CO dissociation on small Co nanoparticles. 63 …”

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

“…[1][2][3][4] Cobalt-based catalysts are the most important formulations regarding the conversion of syngas to synthetic fuels via Fischer-Tropsch synthesis. [5][6][7][8] IR spectroscopy is apowerful technique for investigating the surface sites and the nature of the reaction intermediates, especially because CO is both ar eactant and am olecular probe that can be used to characterize metal surfaces under reaction conditions.I Rs tudies were previously used to investigate the role of formates,w hich had been proposed as ap recursor of methane or methanol. [5][6][7][8] IR spectroscopy is apowerful technique for investigating the surface sites and the nature of the reaction intermediates, especially because CO is both ar eactant and am olecular probe that can be used to characterize metal surfaces under reaction conditions.I Rs tudies were previously used to investigate the role of formates,w hich had been proposed as ap recursor of methane or methanol.…”

Development and Elucidation of Superior Turnover Rates and Selectivity of Supported Molecular Catalysts

“…This technique was also used to study the performance of Co NPs of different sizes (4.3 nm and 9.5 nm), where large differences on the carbon coverage were found . The 4.3 nm catalyst shows a carbon coverage less than one, while larger NPs exhibit a value greater than two.…”

“…The new gas flow system combines two independent plug-flow circuits (reactive (H 2 and CO) and non-reactive (H 2 and He)) with a four-wayv alve, which allows for an easy selection of and switch between specific gas feeds throught he reactor.T he outlet gaseous compositionr ight after the switcho fc ircuits is monitored by an online quadrupole mass spectrometer with an effectivet ime resolution of 2.2 s. The outlet gases could also be sampled by as ynchronized sampling system (VICI-ST12MWE) and analyzed offline with aG C-MS, which provides af ull product distribution. [30][31] Figure 11 As hows the typical MS response to the outlet gases duringb oth the build-up (0-65 s) and steady state (> [29].CopyrightE lsevier. Figure 10.…”