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Co3O4 nanoparticles were supported on different TiO2 polymorphs, namely, rutile, anatase, and a 15 : 85 mixture of rutile and anatase (also known as P25), via incipient wetness impregnation. The Co3O4/TiO2 catalysts were evaluated in the preferential oxidation of CO (CO-PrOx) in a H2-rich gas environment and characterised in situ using PXRD and magnetometry. Our results show that supporting Co3O4 on P25 resulted in better catalytic performance, that is, a higher maximum CO conversion to CO2 of 72.7% at 200 °C was achieved than on rutile (60.7%) and anatase (51.5%). However, the degree of reduction (DoR) of Co3O4 to Co0 was highest on P25 (91.9% at 450 °C), with no CoTiO3 detected in the spent catalyst. The DoR of Co3O4 was lowest on anatase (76.4%), with the presence of TixOy-encapsulated CoOx nanoparticles and bulk CoTiO3 (13.8%) also confirmed in the spent catalyst. Relatively low amounts of CoTiO3 (8.9%) were detected in the spent rutile-supported catalyst, while a higher DoR (85.9%) was reached under reaction conditions. The Co0 nanoparticles formed on P25 and rutile existed in the fcc and hcp crystal phases, while only fcc Co0 was detected on anatase. Furthermore, undesired CH4 formation took place over the Co0 present in the P25- and rutile-supported catalysts, while CH4 was not formed over the Co0 on anatase possibly due to encapsulation by TixOy species. For the first time, this study revealed the influence of different TiO2 polymorphs (used as catalyst supports) on the chemical and crystal phase transformations of Co3O4, which in turn affect its activity and selectivity during CO-PrOx.

The Fischer-Tropsch synthesis as a large-scale industrial process converts a mixture of carbon monoxide and hydrogen in a surface polymerization reaction to mostly hydrocarbons and water. In fact, water is the most abundant product on a per mole basis. The major deactivation mechanisms for cobalt-based catalysts in the Fischer-Tropsch synthesis regarding the active metallic phase are various forms of carbon deposition, sintering, and oxidation to Fischer-Tropsch inactive oxidic phases. In particular high concentrations of the product water may cause oxidation and sintering of the active metallic cobalt phase, but are inherent to high conversion levels in the Fischer-Tropsch synthesis. Not only can cobalt be oxidized to CoO, it may also form mixed metal oxides such as cobalt aluminates in the presence of a metal oxide support. However, literature only provides limited information on the formation and morphology of such metal-support compounds due to the challenging (direct) characterization of these phases in the spent catalysts. Herein, thermodynamic predictions summarize and discuss the feasibility of water-induced deactivation of cobalt-based Fischer-Tropsch catalysts by oxidation. Further, identified mechanisms for hydrothermal sintering and recent findings on water-induced oxidation of metallic cobalt to CoO are discussed. However, the main emphasis of the review concerns the formation of metal-support compounds and the applicability of various in situ and ex situ characterization techniques on their identification. In particular X-ray absorption spectroscopy has recently provided significant insights into the formation of metal-support compounds in (simulated) high conversion Fischer-Tropsch environment, while high resolution microscopy was successfully applied to elucidate corresponding catalyst morphologies.

[EN] Four Mo-based catalysts were prepared via three different synthesis techniques supported on SiO2 and/or SBA-15. By means of complementary in situ characterization techniques, the carburization process and the final characteristics of these catalysts were investigated. Additionally, the four catalysts were evaluated for the activation of CO2 in the absence and presence of H-2 (reverse water-gas shift, RWGS). The results suggest that CO2 reacts via a dissociation on the carbide surface, forming adsorbed oxygen surface species. Severe oxidation of the carbide into its oxidic phases (MoO2 or MoO3) only occurs at temperatures above 850 K in the presence of CO2. O-2 dissociates on the carbide surface when introduced at low concentrations (1 vol %) at room temperature, but when exposed to higher concentrations, a strong exothermic bulk re-oxidation reaction occurs, forming MoO2. All four catalysts show high RWGS activity in terms of CO2 conversions with a minimum CO selectivity of 98% without any signs of bulk catalyst oxidation. Although minimal, the observed deactivation is suggested to be primarily due to phase changes between Mo2C allotropes (beta-phase, oxycarbide, and eta-phase) and/or sintering of the active phase., All members affiliated with the Catalysis Institute and c*change would like to gratefully acknowledge the financial support received from the DST-NRF Centre of Excellence in Catalysis (c*change) and the University of Cape Town (UCT). We acknowledge Diamond Light Source for time on B18 as part of the Block Allocation Group beamtime of the UK Catalysis Hub in December 2018. A special thanks goes out to R. Cerpath and M. Malatji for their contributions in RWGS catalyst testing as part of their B.Sc. final year project; S. Govender, R. Geland, S. Klink, and S. Nyimbinya of the Analytical Laboratory in the Department of Chemical Engineering at UCT for the BET and ICP-OES analysis. M. Jaffer (UCT) for his support with the TEM analysis; M. Waldron for her assistance in the offline Raman analysis; and J. Callison and M. Panchal for their assistance in the offline XAS data acquisition. A. Mun~oz and I. Lopez (ITQ) are acknowledged for technical assistance with in situ Raman studies. We would like to thank the Institute for Beam Physics and Technology (IBPT) for the operation of the storage ring, the Karlsruhe Research Accelerator (KARA).

The effect of both the Fe : Ni ratio (5 to 1 : 1) and the relative Lewis acidity of a metal oxide support on catalytic activity, selectivity and stability was investigated in the CO2 mediated oxidative dehydrogenation of ethane (CO2-ODH). To avoid effects of varying pore sizes, shapes and volumes of the supports, chromia and zirconia overlayers were coated onto a common γ-Al2O3 carrier (CrOx@Al2O3 and ZrOx@Al2O3). Separately, oxidic FexNiy alloy precursor nanoparticles were prepared using a nonaqueous surfactant-free method and deposited by sonication onto the carrier. In comparison to previous studies in the field, this synthesis technique yields closely associated iron and nickel increasing the chances for alloy formation. During reduction, a mixture of a bcc and a fcc alloy phase was formed, with the content of bcc increasing with increasing iron content as predicted by the bulk phase diagram. Upon exposure to carbon dioxide at elevated temperatures, the bcc metallic phase is selectively oxidised to an inverse spinel structure via the dissociation of CO2. When exposed to CO2-ODH conditions, the bare ZrOx@Al2O3 support shows no activity. The presence of FeNi phases increases the conversion of ethane and CO2 marginally ( 80%). The CrOx@Al2O3 support shows some initial activity (XC2H6 90%) but deactivates with time on stream. Comparison of the ethane and carbon dioxide conversions suggests that direct dehydrogenation rather than the oxidative pathway is taking place. When FeNi particles with the highest Fe content are added, the ethane conversion behavior hardly changes, but the CO2 conversion is increased now supporting the stoichiometric CO2-ODH reaction (SC2H4 > 95%). It is therefore evident that a tandem catalyst system between a reducible oxide carrier and the FeNi species is required. Increasing the Ni content results in an increase in activity and stability while changing the dominant reaction pathway to a combination of dry reforming, CO2-ODH and possibly the reverse Boudouard reaction, with the latter countering catalyst deactivation through carbon deposition.

The performance of Mo2C-based catalysts in CO2 assisted oxidative dehydrogenation (CO2-ODH) of ethane was evaluated. Mo2C on SiO2 was synthesized via three different techniques: wet impregnation (WI), hybrid nanocrystal technique (HNC) and sol–gel method (SG) and exposed to the same carburization conditions. In terms of characteristic properties, the allotrope composition was the most affected, with the SG sample containing MoOxCy and the WI and HNC samples containing β-Mo2C. The two different allotropes were suggested to follow different reaction pathways, leading to small differences in the catalytic performance. However, overall, all three catalysts showed a decrease in activity (below 6%) and an increase in C2H4 selectivity (from 60 to 80 C%) with time on stream (TOS). The deactivation mechanism was suggested to be mainly due to oxidation of the carbide to MoOx and carbon deposition. Mo2C was also supported on various metal oxide materials via the wet impregnation technique. Mo2C supported on Al2O3 and ZrO2 increased initial activity (about 8% C2H6 conversion) but a faster deactivation with TOS was observed. Mo2C/Ga2O3 favoured the direct dehydrogenation reaction achieving high C2H4 selectivities (above 80 C%), but deactivation with TOS due to carbon deposition was significant. Mo2C supported on CeO2 and TiO2 had lower activity (about 3% C2H6 conversion). Oxidation to MoO2 and carbon deposition is again suggested to be the main deactivation mechanism. H2 co-feeding, on Mo2C/SiO2 and Mo2C/ZrO2, increased the stability of the catalysts but C2H4 yield was affected (from 5 to 2%). At 17 vol% H2 co-feeding, Mo2C/ZrO2 showed promising catalyst stability over a 20 h period, paralleled by a stable C2H4 yield.

Transition metal alloys are receiving considerable attention in heterogeneous catalysis as they hold promise to combine advantageous properties of the constituting metals and, therefore, provide at...

The Fischer–Tropsch product, water, is regularly hypothesized to be the driving force for catalyst deactivation. Cobalt nanoparticles may be oxidized to CoO, form mixed-metal oxides with supports, or sinter to larger particles. This Comment discusses the feasibility of these deactivation pathways, highlighting the importance of in situ characterization.

The preferential oxidation of CO (CO-PrOx) with co-fed O2 is an attractive route for removing trace amounts of CO in the H2-rich reformate gas prior to being used for power generation in proton-exc...

We have studied the effect of different supports (CeO2, ZrO2, SiC, SiO2 and Al2O3) on the catalytic performance and phase stability of Co3O4 nanoparticles during the preferential oxidation of CO (CO-PrOx) under different H2-rich gas environments and temperatures. Our results show that Co3O4/ZrO2 has superior CO oxidation activity, but transforms to Co0 and consequently forms CH4 at relatively low temperatures. The least reduced and least methanation active catalyst (Co3O4/Al2O3) also exhibits the lowest CO oxidation activity. Co-feeding H2O and CO2 suppresses CO oxidation over Co3O4/ZrO2 and Co3O4/SiC, but also suppresses Co0 and CH4 formation. In conclusion, weak nanoparticle-support interactions (as in Co3O4/ZrO2) favour high CO oxidation activity possibly via the Mars-van Krevelen mechanism. However, stronger interactions (as in Co3O4/Al2O3) help minimise Co0 and CH4 formation. Therefore, this work reveals the bi-functional role required of supports used in CO-PrOx, i.e., to enhance catalytic performance and improve the phase stability of Co3O4.

Only little is known about the formation and morphology of metal-support compounds (MSCs) in heterogeneous catalysis. This fact can be mostly ascribed to the challenges in directly identifying these phases. In the present study, a series of Co/SiO2 model catalysts with different crystallite sizes was thoroughly characterised with focus on the identification of cobalt silicate, which is the expected metal-support compound for this particular catalyst system. The catalysts were exposed to simulated high conversion Fischer-Tropsch environment, i.e. water-rich conditions in the presence of hydrogen. The transformation of significant amounts of metallic cobalt to a hard-to-reduce phase has been observed. This particular MSC, Co2SiO4, was herein identified as needle- or platelet-type cobalt silicate structures by means of X-ray spectroscopy (XAS) and high-resolution scanning transmission electron microscopy (HRSTEM) in combination with elemental mapping. The metal-support compounds formed on top of fully SiO2-encapsulated nanoparticles, which are hypothesised to represent a prerequisite for the formation of cobalt silicate needles. Both, the encapsulation of cobalt nanoparticles by SiO2 \ud via creeping, as well as the formation of these structures, were seemingly induced by high concentrations of water.

Supported nano-sized metal crystallites as catalysts in the Fischer-Tropsch synthesis have become a major research focus due to their high mass specific surface area and resulting lower cost. Such small supported cobalt crystallites have been reported to show a very different resistance with regard to deactivation compared to larger cobalt particles. The Fischer-Tropsch product water is reported to have a severe effect on the deactivation of cobalt-based Fischer-Tropsch catalysts. Compared to other water-induced deactivation mechanisms, hydrothermal sintering of cobalt nanoparticles is fairly well established in literature. A previously hypothesised interconnection between oxidation of cobalt nanoparticles and hydrothermal sintering has – for the first time – been captured in situ in the presented study. High concentrations of water induce oxidation of the cobalt nanoparticles increasing their mobility and resulting in crystallite growth via particle migration and coalescence whilst in the oxidised state. A well-defined model catalyst comprising highly dispersed cobalt nanoparticles on a relatively inert exfoliated graphite support in combination with an in situ magnetometer allowed for these observations, which resulted in irreversible deactivation of the catalyst.

The presented study investigated the effects of temperature (350–650 °C) and gas environment (pure Ar versus a H2O/H2 partial pressure ratio (PH2O/PH2) of 5) on the extent of sintering and oxidation of Al2O3-supported Ni0 nanoparticles (≈4 nm). We note that a PH2O/PH2 of 5 corresponds to a simulated CO conversion of 94% during methanation. Sintering and oxidation were studied using in situ magnetometry, while ex situ TEM analyses confirmed the particle sizes before and after the magnetometry-based experiments. It was found that increasing the temperature from 350 to 650 °C in Ar at atmospheric pressure causes a negligible change to the average size and degree of reduction (DOR) of the starting Ni0 nanoparticles. However, studying the same temperature window under hydrothermal conditions at 10 bar causes significant particle growth (≈9 nm) and the development of a bimodal distribution. Furthermore, the presence of steam decreases the DOR of Ni0 from 86.2% after initial activation to 22.2% due to oxidation. In summary, this study reports on the expected sintering and oxidation of Ni-based catalysts under high CO conversion conditions at elevated temperatures during methanation. Importantly, we were able to demonstrate how magnetometry-based analyses can provide similar size information (and changes thereof) as those observed with TEM but with the added advantage that this information can be obtained in situ.

Pancreatic &beta, cell-specific clock knockout mice develop &beta, cell oxidative-stress and failure, as well as glucose-intolerance. How inflammatory stress affects the cellular clock is under-investigated. Real-time recording of Per2:luciferase reporter activity in murine and human pancreatic islets demonstrated that the proinflammatory cytokine interleukin-1&beta, (IL-1&beta, ) lengthened the circadian period. qPCR-profiling of core clock gene expression in insulin-producing cells suggested that the combination of the proinflammatory cytokines IL-1&beta, and interferon-&gamma, (IFN-&gamma, ) caused pronounced but uncoordinated increases in mRNA levels of multiple core clock genes, in particular of reverse-erythroblastosis virus &alpha, (Rev-erb&alpha, ), in a dose- and time-dependent manner. The REV-ERB&alpha, /&beta, agonist SR9009, used to mimic cytokine-mediated Rev-erb&alpha, induction, reduced constitutive and cytokine-induced brain and muscle arnt-like 1 (Bmal1) mRNA levels in INS-1 cells as expected. SR9009 induced reactive oxygen species (ROS), reduced insulin-1/2 (Ins-1/2) mRNA and accumulated- and glucose-stimulated insulin secretion, reduced cell viability, and increased apoptosis levels, reminiscent of cytokine toxicity. In contrast, low (&lt, 5,0 &mu, M) concentrations of SR9009 increased Ins-1 mRNA and accumulated insulin-secretion without affecting INS-1 cell viability, mirroring low-concentration IL-1&beta, mediated &beta, cell stimulation. Inhibiting nitric oxide (NO) synthesis, the lysine deacetylase HDAC3 and the immunoproteasome reduced cytokine-mediated increases in clock gene expression. In conclusion, the cytokine-combination perturbed the intrinsic clocks operative in mouse and human pancreatic islets and induced uncoordinated clock gene expression in INS-1 cells, the latter effect associated with NO, HDAC3, and immunoproteasome activity.

In this study, the effect of the presence of Pt in supported Co-based Fischer–Tropsch catalysts is investigated. To this end, the effect of the addition of 0.1 wt% Pt to the formulation of Al2O3-supported catalysts containing “large” (≈20 nm) or “small” (≈10 nm) Co3O4 crystallites is presented. The cobalt particle size can be changed by the presence of diethylene glycol (DEG) in Co-nitrate precursor solution. Pt is deposited on the support by following either the sequential deposition order (SDO), according to which Pt is impregnated onto the calcined Co-catalyst, or the reverse sequential deposition order (RSDO), according to which Pt is impregnated onto the support before Co. We show that despite the small amount of Pt used and regardless of the initial Co3O4 crystallite size and of the deposition order of Pt and Co, the catalyst reducibility is significantly improved when Pt is added to the catalyst formulation. Indeed, Pt favors the reduction of the smallest Co oxide particles, which are hardly reducible in the unpromoted samples, thus shifting the average Co0 particle size towards smaller values. In particular, in the case of “large” Co3O4 particles, Pt has a larger effect when added according to the RSDO method, very likely due to the stronger interaction that is established between Pt and Co. In comparison, the sample with smaller Co3O4 particles (prepared with DEG) shows a higher reducibility when prepared according to the SDO method, due to the presence of a significant fraction of small and difficult to reduce Co3O4 particles. The effect of Pt on the catalytic performance depends on a complex interplay involving the catalyst reducibility, number of Co metal sites and size of the Co0 particle aggregates. Pt strongly improves the performance of the samples originating from the larger cobalt oxide crystallites but on the other hand decreases the reactivity of the samples from the smaller particles. This is due to the fact that the small Co0 sites formed in the presence of Pt are in the size-range where the FTS is known to be structure sensitive and the intrinsic activity (TOF) is reduced.

The effectiveness of the addition of diethylene glycol (DEG) to the impregnating solution in synthesizing highly dispersed Co-based catalysts supported on stabilized alumina (Al2O3(s)) is investigated. Both the properties and catalytic performance in the Fischer-Tropsch synthesis (FTS) of the material obtained using DEG (CoDEG/Al2O3(s)) are compared with those of a catalyst with the same formulation but prepared without the addition of DEG in the impregnating solution (Co/Al2O3(s)). When using Co-nitrate as Co-precursor, the addition of DEG leads to a very fast and exothermic decomposition of Co-nitrate into Co oxides during the calcination step. This prevents the agglomeration of Co3O4 particles, thus generating highly dispersed Co3O4 crystallites on the support. In line with the decrease of the Co3O4 crystallites size, the CoDEG/Al2O3(s) catalyst is more difficult to reduce than the Co/Al2O3(s) catalyst. As a result, the metallic surface of the two catalysts is very similar. Nonetheless, when tested in the FTS, the CoDEG/Al2O3(s) catalyst shows CO conversion higher than the Co/Al2O3(s) sample. This is attributed to the high intrinsic activity (i.e. high Turnover Frequency, TOF) of the small Co0 crystallites of the CoDEG/Al2O3(s) catalyst. We explain this result assuming that the combustion phenomenon occurring during the fast calcination induced by the presence of DEG may generate structural defects on the catalyst surface that are beneficial for the FTS. Notably, the product distribution of CoDEG/Al2O3(s) catalyst is only slightly affected.

The Fischer–Tropsch (FT) process, producing long chained waxes and transportation fuels, is competing with fuels derived from crude oils and its profitability is therefore dependent on the global oil price. However, increasing the value of synthesized products could render the profitability of the FTS independent of the common fluctuations in the commodity price (which are mostly due to global political trends and only to a lesser extent due to market requirements). One way to achieve this, is to target the more valuable products of the Fischer–Tropsch spectrum, for example oxygenates. This study investigates the effect of synthesis protocols on the surface characteristics of molybdenum carbide and the use of potassium promoted Mo2C as a catalyst for higher oxygenate (C2+ oxygenates) synthesis in CO hydrogenation. A graphitic surface layer was observed with TEM, XPS and Raman analysis for Mo2C samples carburized at ≥760 °C. The graphitic carbon, blocking active sites and therefore significantly lowering catalytic activity, could be partially removed by means of a temperature programmed hydrogenation, forming methane. An unpromoted β-Mo2C catalyst, carburized at 630 °C, reached CO conversions up to ±40% at the conditions applied. Initial 6.2 wt% K/Mo promotion of the catalyst with potassium showed a significant drop in catalyst activity, however, an increase in potassium content did not further decrease catalyst activity. The selectivity towards oxygenates was enhanced, yet it has a certain optimum with regards to promotor concentration. Simultaneously, the oxygenate distribution shifted towards higher alcohols. The initial methanol content in the total oxygenate product was around 60 C% and decreased to approximately 20 C% upon potassium promotion.

Different supporting procedures were followed to alter the nanoparticle–support interactions (NPSI) in two Co3O4/Al2O3 catalysts, prepared using the reverse micelle technique. The catalysts were tested in the dry preferential oxidation of carbon monoxide (CO-PrOx) while their phase stability was monitored using four complementary in situ techniques, viz., magnet-based characterization, PXRD, and combined XAS/DRIFTS, as well as quasi in situ XPS, respectively. The catalyst with weak NPSI achieved higher CO2 yields and selectivities at temperatures below 225 °C compared to the sample with strong NPSI. However, relatively high degrees of reduction of Co3O4 to metallic Co were reached between 250 and 350 °C for the same catalyst. The presence of metallic Co led to the undesired formation of CH4, reaching a yield of over 90% above 300 °C. The catalyst with strong NPSI formed very low amounts of metallic Co (less than 1%) and CH4 (yield of up to 20%) even at 350 °C. When the temperature was decreased from 350 to 50 °C under the reaction gas, both catalysts were slightly reoxidized and gradually regained their CO oxidation activity, while the formation of CH4 diminished. The present study shows a strong relationship between catalyst performance (i.e., activity and selectivity) and phase stability, both of which are affected by the strength of the NPSI. When using a metal oxide as the active CO-PrOx catalyst, it is important for it to have significant reduction resistance to avoid the formation of undesired products, e.g., CH4. However, the metal oxide should also be reducible (especially on the surface) to allow for a complete conversion of CO to CO2 via the Mars–van Krevelen mechanism.

The inert nature of graphitic samples allows for characterisation of rather isolated supported nanoparticles in model catalysts, as long as sufficiently large inter-particle distances are obtained. However, the low surface area of graphite and the little interaction with nanoparticles result in a challenging application of conventional preparation routes in practice. In the present study, a set of graphitic carbon materials was characterised in order to identify potential support materials for the preparation of model catalyst systems. Various sizes of well-defined Co3O4 nanoparticles were synthesised separately and supported onto exfoliated graphite powder, that is graphite after solvent-assisted exfoliation via ultrasonication resulting in thinner flakes with increased specific surface area. The developed model catalysts are ideally suited for sintering studies of isolated nano-sized cobaltous particles as the graphitic support material does not provide distinct metal-support interaction. Furthermore, the differently sized cobaltous particles in the various model systems render possible studies on structural dependencies of activity, selectivity, and deactivation in cobalt oxide or cobalt catalysed reactions.

The preferential oxidation of carbon monoxide has been identified as an effective route to remove trace amounts of CO (approx. 0.5–1.0 vol%) in the H2-rich reformate gas stream after the low-temperature water–gas shift. Instead of noble metal-based catalysts, Co3O4-based catalysts were investigated in this study as cheaper and more readily available alternatives. This study aimed at investigating the effect of crystallite size on the mass- and surface area-specific CO oxidation activity as well as on the reduction behaviour of Co3O4. Model Co3O4 catalysts with average crystallite sizes between 3 and 15 nm were synthesised using the reverse micelle technique. Results from the catalytic tests revealed that decreasing the size of the Co3O4 crystallites increased the mass-specific CO oxidation activity in the 50–200 °C temperature range. On the other hand, the surface area-specific CO oxidation activity displayed a volcano-type behaviour where crystallites with an average size of 8.5 nm were the most active within the same temperature range. In situ characterisation in the magnetometer revealed that the Co3O4 crystallites are partially reduced to metallic Co above 225 °C with crystallites larger than 7.5 nm showing higher degrees of reduction under the H2-rich environment of CO-PrOx. In situ PXRD experiments further showed the presence of CoO concurrently with metallic fcc Co in all the catalysts during the CO-PrOx runs. In all experiments, the formation of fcc Co coincided with the formation of CH4. Upon decreasing the reaction temperature below 250 °C under the reaction gas, both in situ techniques revealed that the fcc Co previously formed is partially re-oxidised to CoO.

The preferential oxidation (PrOx) of carbon monoxide is an effective process for the removal of trace amounts of CO in a hydrogen-rich gas stream originating from steam reforming or gasification processes. CO can act as catalyst poison in various downstream processes such as the ammonia synthesis or PEM fuel cells for power generation. The effect on activity and selectivity of different cobalt oxide morphologies (cubes, sheets and belts) in Co3O4/SiO2 model catalysts was studied against conventional near-spherical nanoparticles. With a combination of offline and specialized in situ characterisation techniques the stability and catalytic performance of the model catalysts was monitored. With TEM and XRD, the prepared nanosheets and nanobelts were identified as superstructures constituted by small crystallites with similar catalytic activity to conventional nanoparticles. The nanocubes however, consisting of single crystals or at least large crystalline domains, display a superior surface specific CO oxidation activity which is attributed to the preferential exposure of {001} planes. Catalytic sites on these plains seem to support the formation of the Co3+/2+ redox pair required for the underlying Mars-van Krevelen mechanism.

Welcome to Africa was the motto when after more than 100 years the flag ship conference series of the Royal Society of Chemistry, the Faraday Discussions was hosted for the first time on the African Continent. Under the fitting topic ‘Catalysis for Fuels’ over 120 delegates followed the invitation by the conference chair Prof. Graham Hutchings FRS (Cardiff Catalysis Institute), his organizing committee and the co-organizing DST-NRF Centre of Excellence in Catalysis c*change (http://www.cchange.ac.za). In the presentations of 21 invited speakers and 59 posters, cutting edge research in the field of catalysis for fuels, designing new catalysts for synthetic fuels, hydrocarbon conversion in the production of synthetic fuels and novel photocatalysis was presented over the two-day meeting. The scene was set by the opening lecture of Prof. Enrique Iglesias (UC Berkeley) and wrapped-up with the concluding remarks by Philip Gibson (SASOL).

We are presenting the use of an alumina supported FeRh alloy catalyst for the formation of nitrogen containing compounds via the CO hydrogenation in the presence of ammonia. In contrast to previous studies on either similar catalyst systems or on an iron-based catalyst, the prepared FeRh material displays a high selectivity to a single nitrogen-containing compound, acetonitrile. The formation of acetonitrile occurs at the expense of oxygenates, mostly ethanol, which form in the absence of ammonia.

We present a newly developed in situ/operando sample presentation device for radiation based characterization techniques. Although originally designed for use on commercial X-ray diffractometers it has also been successfully used in a high energy light source environment. We could show that the device allows monitoring phase and crystallite size changes at elevated temperatures and pressures under various atmospheres, including corroding gases such as steam. In addition and in contrast to most previously described cells the presented device allows for the collection of fully industrially relevant kinetic data from catalytic processes. As an example we show a comparison of the catalytic performance of a cobalt based Fischer-Tropsch catalyst obtained with the developed device which uses a capillary reactor to a performance test conducted in a standard 1/2” stainless steel laboratory scale reactor.

Using an in house developed in situ magnetometer the passivation in diluted oxygen or pure carbon dioxide of a platinum promoted and silica supported cobalt catalyst was studied. No passivation of cobalt was observed after treatment in CO 2 , neither at 30 °C nor at 150 °C. The magnetic cobalt metal phase content remained constant during these treatments and decreased in the subsequent exposure to air. The catalyst exposed to 1% O 2 in N 2 was stable in air at 30 °C. However, no long-term stability was observed. The magnetic measurements during passivation in 1% O 2 indicate partial oxidation of the nanoparticles in form of a CoO layer. The degree of reduction decreased from 89% to 51%, which corresponds to a theoretical oxide layer thickness of 1.3 nm surrounding the metallic core with a diameter of 9.8 nm. Upon re-reduction full recovery of the metal phase was obtained. The re-reduction occurred at significantly lower temperatures than the reduction of the freshly prepared catalyst or the re-reduction of a reduced catalyst after exposure to air without any passivation.

In the field of heterogeneous catalysis research, in situ and operando characterization techniques, i.e. characterization techniques which can be applied under realistic reaction conditions and ideally on a working catalyst, become essential in order to generate new knowledge and understanding of structure performance relationships. Only this knowledge will enable researchers to develop or rather design new catalysts for existing and novel processes without relying on an 'educated guess' approach. In combination with ever improving theoretical predictions, operando characterization techniques are expected to be the main drivers in catalyst research and associated material science in the foreseeable future. Fischer-Tropsch (FT) catalyst systems, and specifically the iron based catalysts, are highly dynamic under reaction conditions, making deductions on structure-activity relationships difficult when relying on conventional characterization techniques. In addition, various deactivation mechanisms, such as oxidation, poisoning, sintering, attrition and phase separation have been observed. As such, the FT synthesis encompasses several challenges experienced in some form or other in most catalytic applications and material science studies. The present review therefore aims to provide a comprehensive account of characterization techniques employed under (quasi) in situ and operando conditions for FT catalysts. Together with a description of the respective technique and a critical discussion of the employed reaction cell, the actual research conducted is briefly discussed. We hope that this combination will enable readers not only to get a good impression of the capabilities and limitations of the respective technique and available instrumentation but also to understand their applicability in catalysis research and maybe to be inspired to push current boundaries.

The formation of mixed-metal cobalt oxides, representing potential metal-support compounds for cobalt-based catalysts, has been observed at high conversion levels in the Fischer-Tropsch synthesis over metal oxide-supported cobalt catalysts. An often observed increase in the carbon dioxide selectivity at Fischer-Tropsch conversion levels above 80% has been suggested to be associated to the formation of water-gas shift active oxidic cobalt species. Mixed-metal cobalt oxides, namely cobalt aluminate and cobalt titanate, were therefore synthesised and tested for potential catalytic activity in the water-gas shift reaction. We present a preparation route for amorphous mixed-metal oxides via thermal treatment of metal precursors in benzyl alcohol. Calcination of the as prepared nanoparticles results in highly crystalline phases. The nano-particulate mixed-metal cobalt oxides were thoroughly analysed by means of X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, X-ray absorption near edge structure spectroscopy, extended X-ray absorption fine structure, and high-resolution scanning transmission electron microscopy. This complementary characterisation of the synthesised materials allows for a distinct identification of the phases and their properties. The cobalt aluminate prepared has a cobalt-rich composition (Co1+xAl2-xO4) with a homogeneous atomic distribution throughout the nano-particulate structures, while the perovskite-type cobalt titanate (CoTiO3) features cobalt-lean smaller particles associated with larger ones with an increased concentration of cobalt. The cobalt aluminate prepared showed no water-gas shift activity in the medium-shift temperature range, while the cobalt titanate sample catalysed the conversion of water and carbon monoxide to hydrogen and carbon dioxide after an extended activation period. However, this perovskite underwent vast restructuring forming metallic cobalt, a known catalyst for the water-gas shift reaction at temperatures exceeding typical conditions for the cobalt-based Fischer-Tropsch synthesis, and anatase-TiO2. The partial reduction of the mixed-metal oxide and segregation was identified by means of post-run characterisation using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy energy-dispersive spectrometry.

Herein we present a comparative study on the water-induced formation of metal–support compounds from metallic cobalt in a simulated high conversion Fischer–Tropsch environment. Literature on the de...

We present a study in which the suitability of potassium promoted iron-based Fischer–Tropsch (FT) catalysts for the generation of synthetic natural gas additives via the hydrogenation of carbon dioxide through a combined reverse water gas shift (WGS) and FT reaction is studied. Using novel in situ instrumentation based on XRD and magnetometry techniques the reversible conversion of metallic iron to Hagg carbide under reaction conditions and its decomposition in hydrogen could be monitored. The facilitating effect of potassium in the formation of iron carbide could be exposed as function of time on stream. While the FT reaction was reduced in the presence of high potassium loadings the reverse WGS reaction seemed to be unperturbed. A faster activation of an iron phase obtained via the decomposition of iron carbide, compared to the initial activation of a pristine iron phase obtained via the reduction of iron oxide was witnessed.

The effect of ammonia on activity and selectivity of a low temperature, iron-catalyzed slurry phase Fischer–Tropsch process was studied. The ammonia content in the feed was varied systematically from 0 to 10 vol% while the total pressure was adjusted simultaneously in order to keep partial pressures constant. In addition to standard Fischer–Tropsch synthesis (FTS) products, long chained aliphatic amines, nitriles and amides were formed; the latter two product classes had not been observed by others before with iron based catalysts. The selectivities toward nitrogen containing compounds increased with increasing ammonia content while the formation rates of alcohols, aldehydes and organic acids were reduced possibly suggesting that nitrogen containing compounds are formed via oxygenates or their precursors. Common FTS descriptors such as methane selectivity, chain growth probability, olefin to paraffin ratio and double bond shift were largely unaffected at the studied levels of ammonia addition, while the activity at ammonia levels above 2 vol% decreased over and above the intrinsic deactivation rate. Although this deactivation seems reversible upon removal of ammonia from the feed gas, the selectivity is shifted toward higher water gas shift reactivity.

Using well-defined supported cobalt nanocrystallites in a novel in situ sample presentation device for laboratory X-ray diffractometers, we investigated the extensively studied structure sensitivity of Fischer–Tropsch (FT) catalysts under simulated high conversion conditions, that is, at high water to synthesis gas ratios. This study has to be regarded as a further small step toward a full understanding of the various processes governing FT activity and selectivity. We were able to show, for two different crystallite sizes, that water has an overall enhancing effect on carbon monoxide conversion and surface specific turnover frequency on metallic surfaces and improves the overall product selectivity with a decrease of methane selectivity. For small crystallites oxidation was observed at elevated water partial pressures, which caused a decrease of activity. The selectivity to the undesired product methane is suppressed in favor of chain growth. This influence on the selectivity might originate from water-i...

A major obstacle in the development of industrial catalysts is the scalability of both catalyst performance and synthesis. While utilizing pilot-scale test reactors allows for a direct transfer from the development stage to the application, it comes at the cost of flexibility. The amount of catalyst required in a pilot-scale test reactor often surpasses the yields of novel synthesis procedures, requiring extensive scale-up efforts. Here, pilot-scale reactors are combined with small lab-scale reactors, using the example of oxidation of o-xylene to phthalic anhydride.

In recent years, several groups have invested significant research capacity to investigate the effect of the metal crystallite size on the various primary and secondary reactions taking place during the Fischer–Tropsch synthesis. Most publications agree that with decreasing crystallite size (dcryst

The utilization of metal nanoparticles traverses across disciplines and we continue to explore the intrinsic size-dependent properties that make them so unique. Ideal nanoparticle formulation to improve a process’s efficiency is classically presented as exposing a greater surface area to volume ratio through decreasing the nanoparticle size. Although, the physiochemical characteristics of the nanoparticles, such as phase, structure, or behavior, may be influenced by the nature of the environment in which the nanoparticles are subjected1, 2 and, in some cases, could potentially lead to unwanted side effects. The degree of this influence on the particle properties can be size-dependent, which is seldom highlighted in research. Herein we reveal such an effect in an industrially valuable cobalt Fischer–Tropsch synthesis (FTS) catalyst using novel in situ characterization. We expose a direct correlation that exists between the cobalt nanoparticle’s size and a phase transformation, which ultimately leads to catalyst deactivation.

Identifying the active site on the surface of a heterogeneous catalyst is one of the biggest challenges in the field of catalysis research. Especially, in the case of structure sensitive and heterogeneously catalyzed reactions, the knowledge of the active site/ensemble would result in a great advantage in the quest to design tailored catalyst displaying the desired activity and selectivity. In the Fischer–Tropsch synthesis, the multitude of reaction products as well as the large number different reaction pathways does result in additional difficulties in the search for the active site/ensemble. In the here presented work, we were able to conduct a thorough study of the CO hydrogenation reactions on nano-sized alumina supported cobalt crystallite model catalysts. By evaluating the full product spectrum, it was possible to deconvolute the structure sensitivity of the various reactions and to gain further insight into the nature of the present reaction mechanisms. It was therefore possible to measure decreasing carbon monoxide turn over frequency with decreasing cobalt crystallite site, paralleled with an increased selectivity toward methane and branched hydrocarbons at a constant olefin selectivity. Although these trends were observed to be independent of time on stream, the activity did change drastically upon the initial exposure to reaction conditions. CO-TPD studies provided direct evidence for the observed size dependencies.

Highly monodisperse cobalt crystallites, supported on Stöber silica spheres, as model catalysts for the Fischer–Tropsch synthesis were exposed to simulated high conversion environments in the presence and absence of CO utilising an in house developedin situmagnetometer. The catalyst comprising the smallest crystallites in the metallic state (average diameter of 3.2 nm) experienced pronounced oxidation whilst the ratio of H2O to H2was increased stepwise to simulate CO conversions from 26% up to complete conversion. Direct exposure of this freshly reduced catalyst to a high conversion Fischer–Tropsch environment resulted in almost spontaneous oxidation of 40% of the metallic cobalt. In contrast, a model catalyst with cobalt crystallites of 5.3 nm only oxidised to a small extent even when exposed to a simulated conversion of over 99%. The largest cobalt crystallites were rather stable and only experienced measurable oxidation when subjected to H2O in the absence of H2. This size dependency of the stability is in qualitative accordance with reported thermodynamic calculations. However, the cobalt crystallites showed an unexpected low susceptibility to oxidation,i.e.only relatively high ratios of H2O to H2partial pressure caused oxidation. Similar experiments in the presence of CO revealed the significance of the actual Fischer–Tropsch synthesis on the metallic surface as the dissociation of CO, an elementary step in the Fischer–Tropsch mechanism, was shown to be a prerequisite for oxidation. Direct oxidation of cobalt to CoO by H2O seems to be kinetically hindered. Thus, H2O may only be capable of indirect oxidation,i.e.high concentrations prevent the removal of adsorbed oxygen species on the cobalt surface leading to oxidation. However, a spontaneous direct oxidation of cobalt at the interface between the support and the crystallites by H2O forming presumably cobalt silicate type species was observed in the presence and absence of CO. The formation of these metal–support compounds is in accordance with conducted thermodynamic predictions. None of the extreme Fischer–Tropsch conditions initiated hydrothermal sintering. Seemingly, the formation of metal–support compounds stabilised the metallic crystallites and/or higher partial pressures of CO are required to increase the concentration of mobile, cobalt oxide-type species on the metallic surface.

The Faraday Discussion on the design of new heterogeneous catalysts took place from 4-6 April 2016 in London, United Kingdom. It brought together world leading scientists actively involved in the synthesis, characterisation, modelling and testing of solid catalysts, attracting more than one hundred delegates from a broad spectrum of backgrounds and experience levels-academic and industrial researchers, experimentalists and theoreticians, and students. The meeting was a reflection of how big of an impact the ability to control and design catalysts with specific properties for particular processes can potentially have on the chemical industry, environment, economy and society as a whole. In the following, we give an overview of the topics covered during this meeting and briefly highlight the content of each presentation.

To obtain nano-sized metal and metal salt crystallites with a narrow size distribution synthesis methods utilizing water in oil (w/o) microemulsions, i.e. reverse micelles, have been widely applied and reported in literature. In this study we show the effect of support addition at different stages of the reverse micelle based preparation of cobalt oxide on alumina model catalysts. All catalysts were characterized with X-ray powder diffraction and Raman spectroscopy indicating the presence of Co3O4 on the Al2O3 support. Studies of the reduction behaviour and X-ray photoelectron spectroscopy however revealed the presence of difficult to reduce cobalt aluminate species in the samples where the support was added during or shortly after the precipitation step in the synthesis process. It can therefore be assumed that if the alumina support is added to the reverse micelle solution unprecipitated Co2+ ions and partially dissolved Al3+ combine and form cobalt aluminates. In the preparations where the solid cobalt precipitates are recovered from the microemulsion and then supported on the carrier, no metal-aluminate formation could be observed. This study therefore gives important information how metal-support interaction can be affected during catalyst preparation using reverse micelles.

In order to study the role of the crystallite size of an active phase in a catalytic reaction it is of utmost importance to be able to synthesise pure phases of crystallites in the desired size range with a narrow size distribution. In this paper we describe a new method to produce Co3O4 crystallites in the nanometer size range (average sizes: 3–10 nm) utilising reverse micelles as nano reactors. To prepare suitable model catalysts for studies on effects of crystallite size these crystallites can be deposited onto a variety of carriers, in this work an alumina support was used. It is further shown that the supported cobalt oxide crystallites prepared in this study do not undergo extensive sintering under reductive conditions (H2 flow and temperatures between 375 and 450 °C) so that also a series of model catalysts with metallic cobalt crystallites of varied size could be prepared. The resulting metal phase only shows the diffraction pattern of a face-centred cubic (fcc) crystal phase, while normally mixtures of fcc an hcp cobalt were obtained in previous studies. Furthermore, almost complete reduction of the catalyst could be obtained for all crystallite sizes and no Co-aluminate formation was observed. These model catalyst systems allow the study of structure sensitive reactions with an industrially relevant catalyst system in the absence of the commonly encountered difficulties like the formation of strong metal support interactions, co-existence of different metal crystallite phases, an incomplete reducibility and crystallite growth upon exposure to reduction/reaction conditions.

Philip Davies opened the discussion of the introductory lecture by Avelino Corma: Themetal nanoparticles inside the zeolites are in a different environment from those outside. Is there any difference in their chemistry and their catalytic behaviour? Avelino Corma answered: We were not able to determine the differences in reactivity, other than the accessibility of reactants with different sizes. It should be said that we did not use molecules specifically suited for showing potential electronic–entropic differences. I agree that this is an important point to be considered. What we clearly observed is that the clusters inside the channels were stable towards sintering. Cynthia Friend asked: Have you considered the possible effect of ligands bound to your clusters? Have van der Waals’ interactions been explicitly included? Avelino Corma replied: The theoretical calculation of the interactions of nitrobenzene with the nanoparticles includes the interactions with the support and van der Waals’ interactions. In the case of clusters, H2 dissociation has been carried out on isolated Pt, Au and Au-Pt clusters and van der Waals’ interactions were not considered. Graham Hutchings continued: You rightly point out in your design strategy that the adsorption of the reactant is the key factor, and that adsorption occurs.

Metal–support interactions in the form of iron–silicate were investigated by an inverse approach, that is, modification of nano-sized iron oxide with surface silicate groups. The presence of surface silicate groups in the calcined catalyst precursor was confirmed using diffuse reflectance infra-red Fourier transform analysis. The genesis of the various iron phases in the presence of surface silicate groups after H 2 -activation and the Fischer–Tropsch synthesis was followed. The surface silicate groups are preserved after a hydrogen treatment at 350 °C for 16 h, and these surface ligands are associated with the residual iron oxide phase, wustite. During the Fischer–Tropsch synthesis, α-Fe is mostly converted into χ-Fe 5 C 2 , whereas FeO is the main source for e-Fe 2 C. The activity per unit surface area of hexagonal carbide, e-Fe 2 C, is ca. 25% higher than that of χ-Fe 5 C 2 . The presence of surface silicate ligands on e-Fe 2 C results in a further enhancement of the rate per unit surface area of e-Fe 2 C by a factor of ca. 3. This is being ascribed to the enhanced availability of hydrogen on the surface due to the presence of the surface silicate groups, which also results in an increase in the methane selectivity, a decrease in the olefin content and a decrease in formation of branched product compounds.

The selective conversion of syngas to higher alcohols is an attractive albeit elusive route in the quest for effective production of chemicals from alternative carbon resources. We report the tandem integration of solid cobalt Fischer–Tropsch and molecular hydroformylation catalysts in a one-pot slurry-phase process. Unprecedented selectivities (>50 wt %) to C alcohols are achieved at CO conversion levels >70 %, alongside negligible CO side-production. The efficient overall transformation is enabled by catalyst engineering, bridging gaps in operation temperature and intrinsic selectivity which have classically precluded integration of these reactions in a single conversion step. Swift capture of 1-olefin Fischer–Tropsch primary products by the molecular hydroformylation catalyst, presumably within the pores of the solid catalyst is key for high alcohol selectivity. The results underscore that controlled cooperation between solid aggregate and soluble molecular metal catalysts, which pertain to traditionally dichotomic realms of heterogeneous and homogeneous catalysis, is a promising blueprint toward selective conversion processes., This work received funding from the German Ministry for Education and Research (BMBF, 01DG17019 CAT2BIOL) and the European Research Council (ERC-2019-COG 864195, TANDEng). Parts of this research have also received funding from the Spanish Ministry of Science and Innovation (RTI2018-096399-A-100), the EU Horizon 2020 research and innovation programme under Grant Agreement no. 817612 (REDIFUEL) and the Max Planck Society. W.L. acknowledges the “Fuel Science Center”, funded by the German Research Foundation (DFG) (grant Nr. 390919832), for continuing support. Sasol and Eurosupport are thanked for the provision of Al2O3 precursors. Prof. F. Schüth (MPI-KOFO) is gratefully thanked for lab space allocation and supportive access to research instrumentation. A. Gurowski (MPI-CEC), N. Pfänder (MPI-CEC), V. Dietl (MPI-KOFO) and M. Fadlalla (UCT) are acknowledged for contributions to ICP-MS, STEM/EDS, offline GC and 2DGC analyses, respectively. Staff of the EM unit at the UPV are acknowledged for technical assistance with microscopy characterization. Open Access funding enabled and organized by Projekt DEAL.