Capturing the Genesis of an Active Fischer–Tropsch Synthesis Catalyst with Operando X‐ray Nanospectroscopy

Abstract

Astate-of-the-art operando spectroscopic technique is applied to Co/TiO 2 catalysts,which account for nearly half of the worldst ransportation fuels produced by Fischer-Tropsch catalysis.This allows determination of,ataspatial resolution of approximately 50 nm, the interdependence of formed hydrocarbon species in the inorganic catalyst. Observed trends show intra-and interparticular heterogeneities previously believed not to occur in particles under 200 mm. These heterogeneities are strongly dependent on changes in H 2 /CO ratio,but also on changes therebyi nduced on the Co and Ti valence states.W e have captured the genesis of an active FTS particle over its propagation to steady-state operation, in which microgradients lead to the gradual saturation of the Co/TiO 2 catalyst surface with long chain hydrocarbons (i.e., organic film formation).Heterogeneous catalytic reactions such as the Fischer-Tr opsch synthesis (FTS) of long-chain hydrocarbons are dynamic and complex, often comprised of inorganic (catalyst) and organic parts (reactants and products). Conventional and widely applied spectroscopic techniques often focus on either the organic part (e.g., vibrational spectroscopy) or on the inorganic part (e.g., X-ray spectroscopic techniques). The combination of both inorganic and organic information shows great promise to answer long-standing questions about complex catalytic reactions.T he FTS propagates through ac omplex surface polymerization process of adsorbed C 1 reaction intermediates derived from synthesis gas (a mixture of CO and H 2 ). [1][2][3][4][5][6][7] Cobalt-based FTS catalysts are an integral part of this gas-to-liquid (GTL) process because of their high wax selectivity and relatively high stability. [8,9] Theactivation and deactivation of these cobalt nanoparticles supported on an inorganic oxide,such as Al 2 O 3 or TiO 2 ,isbelieved to occur through am ultitude of mechanisms,h owever consensus in literature is often still lacking. While the literature is imbued with proposed deactivation mechanisms, [5,10,11] the equally interesting catalyst activation period is often overlooked. [12,13] During the day(s)-long activation or induction period (which is highly dependent on reaction conditions and the catalyst), FTS catalyst particles are believed to be gradually saturated by afilm of long-chain hydrocarbons,followed by pore filling through which further reactants must diffuse. [12,14,15] The complexity of the FTS process is also captured in the myriad of proposed deactivation mechanisms,w hich are generally related to the conversion of the active phase, considered as metallic cobalt, into an inert phase.F or example,cobalt reoxidation or carburization, [16,17] the formation of support oxide-cobalt species occurring through strong metal-support interactions (SMSI), [8,18,19] the loss of active cobalt surface area arising from crystalline growth (i.e., metal sintering), [11,[20][21][22] and finally fouling for example by hydrocarbon deposition in the form of various carbon species formed at the cob...

In Situ Local Temperature Mapping in Microscopy Nano‐Reactors with Luminescence Thermometry

“…Microelectromechanical systems (MEMS) nano‐reactors have been developed over the last decade to satisfy these requirements. For the STXM experiments described in literature, two generations of nano‐reactor can be distinguished. Firstly, the monolithic nano‐reactor, a single MEMS device with a gas channel that passes between two membranes and a micro‐heater spiral on one of the membranes.…”

“…A promising method for the investigation of both organic and inorganic parts of a catalyst system on the single particle level is scanning transmission X‐ray microscopy (STXM), especially in combination with mass spectrometry (MS) or gas chromatography (GC) . STXM is a so‐called micro‐spectroscopy technique, which combines microscopy with X‐ray absorption spectroscopy and allows studying a wide variety of chemical elements by their X‐ray absorption near edge structure (XANES, Figure a and 1b) including carbon in the organic fraction of the catalytic process.…”

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X‐ray Probes

“…Chemie the means to map the composition and structure of metal catalyst particles and single crystals under real conditions,for example by (S)TXM, [77,78] m-XRD-CT, [46] or CDI, [47] uncovering particle heterogeneities commonly present in heterogeneous catalysts. [79,80] As the spatial resolution of state-of-theart X-ray nanoscopes (ca.…”

Observing How Fischer-Tropsch Synthesis Catalysts Work at the Nanoscale via Operando STXM

“…In a recent paper published in Angewdte Chemie, Weckhuysen and coworkers made a further step toward the nature of another industrially important FTS catalyst, Co/TiO 2 , and reported a direct operando observation of an FTS process on this catalyst via the STXM method. 10 By carefully designing a state-of-the-art micro-electromechanical system cell with a 15 nm CVD SiN x membrane window, they showed that the instrument achieved sufficient transmittance for the catalyst-grains images in the range of Co/ Ti L-edges and C K-edge with a spatial resolution of 50 nm. By analyzing the spectra of different atom edges at specific fine zones, they successfully monitored the tempo-spatial evolution of the catalyst surface on the basis of the Co and Ti edges.…”

“…In the in situ STXM study, 10 three Co particles on the commercial Co/TiO 2 grains were observed by STXM under 1-4 bar with different CO/H 2 ratios. The analysis of three spatially isolated Co particles after hydrogen treatment demonstrated that the reduction degree of Co particles was influenced by the reduction conditions.…”