The fundamentals of structure sensitivity and promoter effects in the Fischer−Tropsch synthesis of lower olefins have been studied. Steady state isotopic transient kinetic analysis, switching 12 CO to 13 CO and H 2 to D 2 , was used to provide coverages and residence times for reactive species on supported iron carbide particles of 2−7 nm with and without promoters (Na + S). CO coverages appeared to be too low to be measured, suggesting dissociative adsorption of CO. Fitting of CH 4 response curves revealed the presence of parallel side-pools of reacting carbon. CH x coverages decreased with increasing particle size, and this is rationalized by smaller particles having a higher number of highly active low coordination sites. It was also established that the turnover frequency increased with CH x coverage. To calculate H coverages, new equations were derived to fit HD response curves, again leading to a parallel side-pool model. The H coverages appeared to be lower for bigger particles. The H coverage was suppressed upon addition of promoters in line with lower methane selectivity and higher lower olefin selectivity. Density functional theory (DFT) was applied on H adsorption for a fundamental understanding of this promoter effect on the selectivities, with a special focus on counterion effects. Na 2 S is a better promoter than Na 2 O due to both a larger negative charge donation and a more effective binding configuration. On the unpromoted Fe 5 C 2 (111) surface, H atoms bind preferably on C after dissociation on Fe. On Na 2 S-promoted Fe 5 C 2 surfaces, adsorption on carbon sites weakens, and adsorption on iron sites strengthens, which fits with lower H coverage, less CH 4 formation, and more olefin formation.

The Fischer–Tropsch Synthesis converts synthesis gas from alternative carbon resources, including natural gas, coal, and biomass, to hydrocarbons used as fuels or chemicals. In particular, iron-based catalysts at elevated temperatures favor the selective production of C2–C4 olefins, which are important building blocks for the chemical industry. Bulk iron catalysts (with promoters) were conventionally used, but these deactivate due to either phase transformation or carbon deposition resulting in disintegration of the catalyst particles. For supported iron catalysts, iron particle growth may result in loss of catalytic activity over time. In this work, the effects of promoters and particle size on the stability of supported iron nanoparticles (initial sizes of 3–9 nm) were investigated at industrially relevant conditions (340 °C, 20 bar, H2/CO = 1). Upon addition of sodium and sulfur promoters to iron nanoparticles supported on carbon nanofibers, initial catalytic activities were high, but substantial deactivation was observed over a period of 100 h. In situ Mössbauer spectroscopy revealed that after 20 h time-on-stream, promoted catalysts attained 100% carbidization, whereas for unpromoted catalysts, this was around 25%. In situ carbon deposition studies were carried out using a tapered element oscillating microbalance (TEOM). No carbon laydown was detected for the unpromoted catalysts, whereas for promoted catalysts, carbon deposition occurred mainly over the first 4 h and thus did not play a pivotal role in deactivation over 100 h. Instead, the loss of catalytic activity coincided with the increase in Fe particle size to 20–50 nm, thereby supporting the proposal that the loss of active Fe surface area was the main cause of deactivation.

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Due to the surge of natural gas production, feedstocks for chemicals shift towards lighter hydrocarbons, particularly methane. The success of a Gas-to-Chemicals process via synthesis gas (CO and H2) depends on the ability of catalysts to suppress methane and carbon dioxide formation. We designed a Co/Mn/Na/S catalyst, which gives rise to negligible Water-Gas-Shift activity and a hydrocarbon product spectrum deviating from the Anderson–Schulz–Flory distribution. At 240 °C and 1 bar, it shows a C2-C4 olefins selectivity of 54%. At 10 bar, it displays 30% and 59% selectivities towards lower olefins and fuels, respectively. The spent catalyst consists of 10 nm Co nanoparticles with hcp Co metal phase. We propose a synergistic effect of Na plus S, which act as electronic promoters on the Co surface, thus improving selectivities towards lower olefins and fuels while largely reducing methane and carbon dioxide formation.

The transition from integrated petrochemical complexes toward decentralized chemical plants utilizing distributed feedstocks calls for simpler downstream unit operations. Less separation steps are attractive for future scenarios and provide an opportunity to design the next-generation catalysts, which function efficiently with effluent reactant mixtures. The methanol to olefins (MTO) reaction constitutes the second step in the conversion of CO 2 , CO, and H 2 to light olefins. We present a series of isomorphically substituted zeotype catalysts with the AEI topology (MAPO-18s, M = Si, Mg, Co, or Zn) and demonstrate the superior performance of the M(II)-substituted MAPO-18s in the conversion of MTO when tested at 350 °C and 20 bar with reactive feed mixtures consisting of CH 3 OH/CO/CO 2 /H 2 . Co-feeding high pressure H 2 with methanol improved the catalyst activity over time, but simultaneously led to the hydrogenation of olefins (olefin/paraffin ratio < 0.5). Co-feeding H 2 /CO/CO 2 /N 2 mixtures with methanol revealed an important, hitherto undisclosed effect of CO in hindering the hydrogenation of olefins over the Brønsted acid sites (BAS). This effect was confirmed by dedicated ethene hydrogenation studies in the absence and presence of CO co-feed. Assisted by spectroscopic investigations, we ascribe the favorable performance of M(II)APO-18 under co-feed conditions to the importance of the M(II) heteroatom in altering the polarity of the M–O bond, leading to stronger BAS. Comparing SAPO-18 and MgAPO-18 with BAS concentrations ranging between 0.2 and 0.4 mmol/g cat , the strength of the acidic site and not the density was found to be the main activity descriptor. MgAPO-18 yielded the highest activity and stability upon syngas co-feeding with methanol, demonstrating its potential to be a next-generation MTO catalyst.

Colloidal synthesis routes have been recently used to fabricate heterogeneous catalysts with more controllable and homogeneous properties. Herein a method was developed to modify the surface composition of colloidal nanocrystal catalysts and to purposely introduce specific atoms via ligands and change the catalyst reactivity. Organic ligands adsorbed on the surface of iron oxide catalysts were exchanged with inorganic species such as Na2S, not only to provide an active surface but also to introduce controlled amounts of Na and S acting as promoters for the catalytic process. The catalyst composition was optimized for the Fischer–Tropsch direct conversion of synthesis gas into lower olefins. At industrially relevant conditions, these nanocrystal-based catalysts with controlled composition were more active, selective, and stable than catalysts with similar composition but synthesized using conventional methods, possibly due to their homogeneity of properties and synergic interaction of iron and promoters.

The Fe‐catalyzed Fischer–Tropsch to olefins (FTO) synthesis is a non‐oil‐based route for the production of C2–C4 olefins. The understanding of the interplay between the catalytically active species, promoters, and support materials has improved over the last years, but the nanostructures of the various supports used are often not comparable. Several ordered mesoporous materials with a comparable pore size and pore symmetry are used as model supports for Fe‐based FTO catalysts. Ammonium iron citrate is used as the Fe source for all supports, and Na and S are added as promoters. The formation of catalytically active iron carbide species is suppressed within the strongly interacting mesoporous silica support, but the weakly interacting carbon and silicon carbide supports yield highly active FTO catalysts. Carbon‐supported catalysts show a high selectivity towards lower olefins, low methane production, and stable operation for up to 140 h under industrially relevant FTO conditions.

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