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Heterogeneous supported catalysts are often synthesized by impregnation or precipitation methods. Recently, melt infiltration has emerged as an alternative method that allows high metal loadings and eliminates the need for a solvent, but challenges arise regarding control over the particle size and distribution. In this work, melt infiltration for the synthesis of supported silver catalysts is explored. The narrow pore size distribution of the chosen ordered mesoporous silica support, SBA-15, allowed in depth in-situ and ex-situ characterization of the infiltration of the precursor, molten silver nitrate, into the support and its subsequent decomposition to form metallic silver nanowires or nanoparticles. The heat treatment parameters during decomposition played a key role in determining whether nanowires or nanoparticles were formed. The supported silver catalysts containing high silver weight loadings were investigated in the selective hydrogenation of cinnamaldehyde, where the silver nanowires showed superior activity and selectivity over the nanoparticles. Hence, melt infiltration shows great promise for the synthesis of supported silver catalysts containing high silver weight loadings, which are applicable in, e.g., selective oxidation or hydrogenation reactions.

Background Recipient selection for liver transplantation in hepatocellular carcinoma (HCC) is based primarily on criteria affecting the chance of long-term success. Here, the relationship between pretransplant bridging therapy and long-term survival was investigated in a subgroup analysis of the SiLVER Study. Methods Response to bridging, as defined by comparison of imaging at the time of listing and post-transplant pathology report, was categorized into controlled versus progressive disease (more than 20 per cent tumour growth or development of new lesions). Results Of 525 patients with HCC who had liver transplantation, 350 recipients underwent pretransplant bridging therapy. Tumour progression despite bridging was an independent risk factor affecting overall survival (hazard ratio 1.80; P = 0.005). For patients within the Milan criteria (MC) at listing, mean overall survival was longer for those with controlled versus progressive disease (6.8 versus 5.8 years; P

The effect of oxidation of a carbon nanotube (CNT) support on the structure and catalytic performance in the Fischer-Tropsch (FT) synthesis of pre-synthesized cobalt nanocrystals (NC) has been investigated. 6 nm CoO-NC were prepared using colloidal techniques and impregnated on pristine and surface-oxidized CNT. The CoO-NC on pristine CNT were reduced completely to Co, while ∼50 % CoO reduction was observed on oxidized CNT (oxCNT), indicating a stronger Co-support interaction on oxCNT. In FT, the turnover frequency (TOF) after 100 h was exceptionally high on pristine CNT (150·10−3 s-1) against 63·10−3 s-1 on oxCNT. In the initial stage of FT, the TOF was 35 % lower on oxCNT than on pristine CNT, which matched with 32 % lower crystallinity of cobalt determined using in situ XRD. Furthermore, deactivation was observed mainly on oxCNT. These results demonstrate the large impact of the support on the structure and performance of nanocrystal-based catalysts.

Stability of metal nanoparticles under reaction conditions is crucial in many catalytic processes. Nickel-based catalysts often encounter severe particle growth in the presence of carbon monoxide due to the formation and migration of nickel carbonyl. In this research, we showed that the reduction temperature of nickel oxide supported on niobia (Nb2O5) influenced the stability of the resulting nickel catalyst during subsequent carbon monoxide hydrogenation. Low reduction temperatures resulted in high initial nickel-normalized activity towards long-chain hydrocarbons (C5+), but fast deactivation throughout the experiment. High reduction temperatures led to a shift in product distribution towards shorter hydrocarbons and a decreased initial nickel-normalized activity, while during the first hours of the experiment an increase in turnover frequency and nickel-normalized activity was observed, resulting eventually in a stable catalytic performance. Electron microscopy analysis revealed extensive particle growth after catalysis when the catalyst had been reduced at low temperatures and no significant changes in particle size when reduced at high temperatures. By use of in-situ FT-IR spectroscopy, nickel subcarbonyl species which are precursors of volatile nickel tetracarbonyl were detected on Ni/Nb2O5 after low temperature reduction and exposure to CO, but not after high temperature reduction. Hence, particle growth is explained by the formation and diffusion of nickel carbonyl and subsequent Ostwald ripening, that leads to larger nickel particles with concomitant decrease in nickel-normalized activity. The stability of the catalyst reduced at high temperature was linked to the formation of niobium suboxides and their partial coverage of the nickel particles limiting the formation of nickel carbonyl and slowing down particle growth.

Using colloidal iron oxide nanoparticles with organic ligands, anchored in a separate step from the supports, has been shown to be beneficial to obtain homogeneously distributed metal particles with a narrow size distribution. Literature indicates that promoting these particles with sodium and sulfur creates an active Fischer-Tropsch catalyst to produce olefins, while further adding an H-ZSM-5 zeolite is an effective way to obtain aromatics. This research focused on the promotion of iron oxide colloids with sodium and sulfur using an inorganic ligand exchange followed by the attachment to H-ZSM-5 zeolite crystals. The catalyst referred to as FeP/Z, which consists of iron particles with inorganic ligands attached to a H-ZSM-5 catalyst, was compared to an unpromoted Fe/Z catalyst and an Fe/Z-P catalyst, containing the colloidal nanoparticles with organic ligands, promoted after attachment. A low CO conversion was observed on both FeP/Z and Fe/Z-P, originating from an overpromotion effect for both catalysts. However, when both promoted catalysts were washed (FeP/Z-W and Fe/Z-P-W) to remove the excess of promoters, the activity was much higher. Fe/Z-P-W simultaneously achieved low selectivity toward methane as part of the promoters were still present after washing, whereas for FeP/Z-W the majority of promoters was removed upon washing, which increased the methane selectivity. Moreover, due to the addition of Na+S promoters, the iron nanoparticles in the FeP/Z(-W) catalysts had grown considerably during catalysis, while those in Fe/Z-P(-W) and Fe/Z(-W) remained relatively stable. Lastly, as a large broadening of particle sizes for the used FeP/Z-W was found, where particle sizes had both increased and decreased, Ostwald ripening is suggested for particle growth accelerated by the presence of the promoters.

The effect of oxidative treatments on the depostion of cobalt nanocrystals (Co-NC) onto a support and subsequent ligand removal was investigated. Deposition of ϵ-cobalt NC led to extensive clustering of NC and low Fischer-Tropsch synthesis activity. Low-temperature oxidation of ϵ-cobalt NC resulted in a very uniform CoO-NC distribution and high activity whereas high-temperature oxidation to Co3O4 led to less uniform NC distributions and lower activity.

The production of dimethyl ether (DME) as compared to methanol from synthesis gas allows for increased conversions in a single pass. A challenge in this process is the combination of methanol synthesis and dehydration functionalities in a single catalyst without mutual negative interference of their performances. Here, we studied the use of hydrated niobium pentoxide (Nb2O5·nH2O) and niobium phosphate (NbOPO4) in combination with a copper-based methanol synthesis catalyst in the direct synthesis of DME, while gamma-alumina (γ-Al2O3) was used as a reference material. The three solid acids combined with the copper-based catalyst proved active and selective in the production of DME, however all of them showed some degree of deactivation throughout the reaction. Characterization of the used catalysts pointed out that while the γ-Al2O3-based mixture deactivated most likely due to coke deposition on the alumina and structural changes in the methanol synthesis catalysts, the Nb2O5·nH2O and NbOPO4-based catalysts lost activity probably as a result of copper migration from the methanol synthesis catalyst to the acid component. In view of the high volume-based activity of the Nb-based solid acids it is concluded that these are promising components for the direct catalytic conversion of synthesis gas to DME.

Structure and catalytic performance of niobia-supported cobalt catalysts were studied based on crystal phase, porosity and cobalt loading. Crystalline niobia as support proved to be a prerequisite to obtain highly active and selective Co/niobia Fischer–Tropsch catalysts, whereas amorphous niobia showed minimal activity. Crystallization changed the porous morphology of Nb 2 O 5 · n H 2 O resulting in a dense material with low specific pore volume and specific surface area. Multiple impregnations on crystalline Nb 2 O 5 were necessary to achieve cobalt loadings higher than 6 wt.%; this led to larger cobalt particles, diminished interaction of cobalt with niobia and therefore decreased activity per unit weight of cobalt and C 5+ selectivity. Carbon deposition via sucrose pyrolysis was employed in order to partly maintain the porosity during crystallization. The obtained porous crystalline niobia was used as support for cobalt catalysts with higher metal loadings. STEM-EDX mapping characterization of the catalysts provided unique information for this kind of materials, e.g. cobalt distribution and particle size. The catalysts showed high cobalt-normalized catalytic activity and C 5+ selectivity for the Fischer–Tropsch synthesis under industrially relevant conditions. Moreover, higher cobalt loadings led to an increased catalyst-weight normalized catalytic activity.

In the epoxidation of ethylene, catalyzed by supported Ag particles, the support plays not only a beneficial role, but can also negatively impact the selectivity to ethylene oxide. Especially high surface area supports, and supports containing acid groups, seem detrimental for the selectivity, which is attributed to secondary reactions on the support surface. We prepared Ag nanoparticles on supports with a wide range of specific surface areas and different chemical nature, but with similar Ag metal loading and particle size. Indeed, a strong dependence of selectivity on both the specific surface area, and the chemical nature of the oxide support was found, with α-Al 2 O 3 giving much more selective catalysts than SiO 2 . Furthermore, the conversion was an important factor in determining the selectivity, while on the other hand the support had no influence at all on the ethylene conversion. We described our experimental selectivities with a reaction model that used the rate constant for the secondary reaction of oxidation of ethylene oxide to carbon dioxide and water as the only variable parameter. The model was able to adequately describe the experimental results. It gave insight into the dependence of selectivity on conversion, how the secondary reaction depended on the chemical nature of the support, and how its rate scaled linearly with the support's specific surface area. Building on this insight we modified a SiO 2 support to passivate its OH-groups, which indeed yielded a 94% decrease in the rate of the secondary reaction, performing even better than α-Al 2 O 3 with similar specific surface area would. We have shown that the selectivity towards ethylene oxide is dependent on a metal specific, intrinsic selectivity, and the decrease in selectivity with conversion to be support dependent. This decrease is caused by the isomerization of ethylene oxide, which is found to be first order in ethylene oxide and the active sites on the catalyst support.

In this study Co/Nb2O5 catalysts and the effect of Pt-promotion thereon are investigated in comparison with γ-Al2O3- and α-Al2O3-supported catalysts for the Fischer Tropsch (FT) synthesis. Upon Pt-promotion of Co/Nb2O5 the cobalt-weight normalized FT activity was found to increase by a factor of 2.4, while the high C5+ selectivity of 85 wt% was maintained. Based on environmental TEM results no indications were found that Pt affected the cobalt particle size in Co/Nb2O5 catalysts. A kinetic study indicates an increased number of active sites upon Pt-promotion whereas Steady-State Isotopic Transient Kinetic Analysis experiments show that a combination of an increased number of active sites and an increased turnover frequency is at the origin of the enhanced activity in Co/Nb2O5 catalysts upon Pt-promotion. Pt was tentatively proposed to bring about more efficient promotion of Co by NbOx being present as smaller clusters.

Synthesis gas conversion to short olefins and aromatics using bifunctional catalysts has gained much attention in recent years. Here, we study the interaction between the components of bifunctional catalysts to design a more stable catalyst system. Mixing α-alumina supported iron (-carbide) promoted with sodium and sulfur with an H-ZSM-5 zeolite to convert synthesis gas to aromatics and short olefins we observed selectivity loss of the iron (-carbide) catalyst as well as the acid function. This was displayed by increasing methane and decreasing aromatics selectivity when the two individual catalysts were mixed in close proximity. We introduced different approaches to understand this selectivity related deactivation. Larger spatial separation of the iron and zeolite allowed a more stable system with constant methane and aromatics selectivity. Alternatively, iron supported on carbon nano tubes mixed with the zeolite in close proximity did not display selectivity related deactivation. We conclude that the selectivity loss was caused by migration of sodium ions that were used next to sulfur as promoters on the iron catalyst over the α-alumina support to the zeolite, which was supported by XPS model experiments. This migration seems hindered on carbon supported iron catalysts.