Abstract: Mn and Li promoted Rh catalysts supported on SiO₂ with a thin TiO₂ layer were synthesized by stepwise incipient wetness impregnation approach. The thin TiO₂ layer on the surface of SiO₂ was proved to stabilize those small Rh nanoparticles and hinder their agglomeration. The reducibility of Rh on these catalysts depends on Rh particle size as well as the position of manganese oxide, and large Rh nanoparticles with MnO on Rh nanoparticles can be only reduced at an elevated temperature. Catalyst with large Rh particles exhibits a higher CO conversion and higher products selectivity towards long chain hydrocarbons and C2-oxygenates at the expense of decreasing methane formation than a similar catalyst with smaller Rh particles. This was attributed to the synergistic effect of Mn and Li promotion and molar ratio between Rh⁰ and Rh^δ+ sites on the surface of Rh nanoparticles. Moreover, Rh nanoparticles on MnO are proved to be more efficient in promoting hydrogenation of acetaldehyde to ethanol than its counterpart with MnO on Rh nanoparticles. Finally, in order to target high C2-oxygenates selectivity, low reaction temperature together with a low H₂/CO ratio in the feed is recommended. Graphic Abstract: [Figure not available: see fulltext.].

A membrane reactor containing an immobilized heterogeneous catalyst is an alternative for traditional homogeneous-based catalyzed transesterification for biodiesel production. Major problems in homogeneous catalysis are related to catalyst recuperation and soap formation, which can be overcome by using heterogeneous catalysts. Conversion can be increased by a combination of reaction and separation, using membranes with a specific pore size. The aim of this work was to study the performance of different membrane reactors combined with heterogeneous catalysis. The main objectives were: to identify a proper catalyst, to choose the proper immobilization technique, to establish the membrane with the adequate pore size, and to control the reaction and separation process. Amberlyst®15 with acid sites and different types of strontium oxide with basic sites were tested as heterogeneous catalysts. Strontium oxide provided the highest sunflower oil conversion (around 93%) and was easy to immobilize. Two catalytic membrane reactor configurations were investigated, thus confirming the production of several types of methyl esters. The configuration comprising the physical immobilization of the catalyst over the membrane reached a methyl ester yield of > 90 wt%.

Huge efforts have been done in the last years on electrochemical and photoelectrochemical reduction of CO ₂ to offer a sustainable route to recycle CO ₂ . A promising route is to electrochemically reduce CO ₂ into CO which, by combination with hydrogen, can be used as a feedstock to different added-value products or fuels. Herein, perpendicular oriented TiO ₂ nanotubes (NTs) on the electrode plate were grown by anodic oxidation of titanium substrate and then decorated by a low loading of silver nanoparticles deposited by sputtering (i.e. Ag/TiO ₂ NTs). Due to their quasi one-dimensional arrangement, TiO ₂ NTs are able to provide higher surface area for Ag adhesion and superior electron transport properties than other Ti substrates (e.g. Ti foil and TiO ₂ nanoparticles), as confirmed by electrochemical (CV, EIS, electrochemical active surface area) and chemical/morphological analysis (FESEM, TEM, EDS). These characteristics together with the role of the TiO ₂ NTs to enhance the stability of CO ₂ ^·- intermediate formed due to titania redox couple (Ti ^IV /Ti ^III ) lead to an improvement of the CO production in the Ag/TiO ₂ NTs electrodes. Particular attention has been devoted to reduce the loading of noble metal in the electrode(14.5 %w/%w) and to increase the catalysts active surface area in order to decrease the required overpotential.

We describe the co-current flow pattern of gas and liquid through micro-fabricated beds of solid and pillars under variable (i) capillary number, (ii) contact angle or wettability and (iii) pillar arrangement, i.e. modifying the distance between pillars or their size and comparing regular with more chaotic systems. Laser-induced fluorescent microscopy and image analysis are used to study the hydrodynamic interactions in terms of dynamics, liquid hold-up, and gas-liquid interfacial area per reactor volume. Those parameters provide insights into the multiphase flow patterns in these systems, how to control them, maximize mass transfer rate and unlock the potential of microreactors to reveal further intrinsic information.

The influence of potassium in Rh on a lanthium promoted zirconia stablised ceria (CZ) catalysts was studied toward NO_xreduction reactivity and selectivity. The results are compared with a Rh/CZ catalyst. The samples were characterised by N₂ adsorption, XRD, SEM, ICP, and H₂-TPR. The study highlighted the importance of stored NO_x regeneration over potassium in determining the overall performance of the Rh/K/CZ catalyst. The NO_x stored over Rh/K/CZ in the previous NO gas stream cannot be regenerated sufficiently during the C₃H₆ gas stream, and stored NO_xgradually decreased from one cycle to the next, resulting in deteriorating performance of Rh/K/CZ. Besides, problem of NO_x slip, the formation of both NH₃ and N₂O (selectivities up to 30% for each side product) were observed by the addition of potassium into the Rh/CZ catalyst system, depending on the reaction conditions applied and the severity of the catalyst deactivation.

In this study, the role of the noble metals Pt and Rh (0.5 wt.%) for the selective reduction of NO into N₂ is evaluated by the transient TAP technique and in-situ spectroscopy using a commercial stable ceria support (denoted as CZ) and applying isotopically labelled ¹⁵NO and ¹⁸O₂. The transient operation was mimicked by multi-pulse oxidation (using O₂ or NO) and reduction cycles (using CO, H₂, C₃H₆ and C₃H₈), while following quantitatively the catalyst and reactants response. Pt and Rh significantly lowered the temperature of CZ reduction. CO and H₂ only reduce the surface of CZ, while a 2.5 times deeper reduction was achieved by the hydrocarbons C₃H₆ and C₃H₈, removing also lattice oxygen. Pt and Rh also promoted carbon deposition after surface reduction. Rh was a more active promoter than Pt, while propene was more reactive than propane over both metals. During the NO reduction the pre-reduced CZ support became gradually re-oxidised and after filling 70–80% of the oxygen vacancies the NO started to appear in the product mixture. In the presence of carbon deposits the lattice oxygen of the CZ reacted with the carbon keeping the CZ in a reduced state, extending the NO decomposition process as long as the carbon was present. The reduction of NO over pre-reduced noble metal/CZ showed a selective formation N₂, while N₂O and NO₂ were never observed. During the NO reduction process some unidentified N-species remained on the catalyst, the amount depending on the type of catalyst, but finally all nitrogen was released as N₂. The presence of the noble metal led less unidentified N-species on the CZ surface and to a faster N₂ formation rate than that over the bare CZ.

Ethylbenzene oxidative dehydrogenation over γ-alumina under in situ conditions has revealed that the catalyst recovers fully the original conversion and selectivity under steady state conditions. In the transition state, the reactivated catalyst achieved the steady state conditions faster. This was supported by the physico-chemical characterisation that revealed pore widening due to crystallite sintering during the reactivation, which has a beneficial effect. The excellent stability after the reactivation recycle, as well as along the run, shows the great promise of this catalyst.

Toyota's Di-Air DeNO_x system is a promising DeNO_x system to meet NO_x emission requirement during the real driving, yet, a fundamental understanding largely lacks, e.g. the benefit of fast frequency fuel injection. Ceria is the main ingredient in Di-Air catalyst composition. Hence, we investigated the reduction of ceria by reductants, e.g. CO, H₂, and hydrocarbons (C₃H₆ and C₃H₈), with Temporal Analysis of Product (TAP) technique. The results show that the reduction by CO yielded a faster catalyst reduction rate than that of H₂. However, they reached the same final degree of ceria reduction. Hydrocarbons generated almost three times deeper degree of ceria reduction than that with CO and H₂. In addition, hydrocarbons resulted in carbonaceous deposits on the ceria surface. The total amount of converted NO over the C₃H₆ reduced sample is around ten times more than that of CO. The deeper degree of reduction and the deposition of carbon by hydrocarbon explain why hydrocarbons are the most powerful reductants in Toyota's Di-Air NO_x abatement system.

Oxygen defects in reduced ceria are the catalytic sites for the NO reduction into N₂ in the Toyota Di-Air DeNO_x abatement technology. Traces of NO (several hundred ppm) have to compete with the excess amount of other oxidants, e.g., 5% CO₂ and 5% O₂, in an exhaust gas of a lean burn (diesel) engine. The reactivities of CO₂ and NO over a reduced ceria and noble metal loaded reduced ceria have been investigated under ultra-high vacuum system in TAP and under atmosphere pressure in in-situ Raman and flow reactor set-up. The results showed that CO₂ was a mild oxidant which was able to oxidise the oxygen defects, but hardly oxidised deposited carbon over both ceria and noble metal loaded ceria. NO was a stronger oxidant and more efficient in refilling the oxygen defects and able to convert the deposited carbon, which acted as buffer reductant to extend the NO reduction time interval. NO was selectively and completely converted into N₂. The presence of excess CO₂ hardly affected the NO reduction process into N₂.

Background: Inhalation of particulate matter, as part of air pollution, is associated with increased morbidity and mortality. Nanoparticles (< 100nm) are likely candidates for triggering inflammatory responses and activation of coagulation pathways because of their ability to enter lung cells and pass bronchial mucosa. We tested the hypothesis that bronchial segmental instillation of carbon nanoparticles causes inflammation and activation of coagulation pathways in healthy humans in vivo. Methods: This was an investigator-initiated, randomized controlled, dose-escalation study in 26 healthy males. Participants received saline (control) in one lung segment and saline (placebo) or carbon nanoparticles 10μg, 50μg, or 100μg in the contra-lateral lung. Six hours later, blood and bronchoalveolar lavage fluid (BALF) was collected for inflammation and coagulation parameters. Results: There was a significant dose-dependent increase in blood neutrophils (p=0.046) after challenge with carbon nanoparticles. The individual top-dose of 100μg showed a significant (p=0.05) increase in terms of percentage neutrophils in blood as compared to placebo. Conclusions: This study shows a dose-dependent effect of bronchial segmental challenge with carbon nanoparticles on circulating neutrophils of healthy volunteers. This suggests that nanoparticles in the respiratory tract induce systemic inflammation. Trial registration: Dutch Trial Register no. 2976. 11 July 2011. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2976

Currently commercial NO_x removal (DeNO_x) abatement systems for lean-burn engines exceed regulation limits on the road for NO_x emissions. Commercial DeNO_x catalysts exhibit poor performance in the selective conversion of NO to N₂, especially at high temperature and high gas hourly space velocities (GHSV). In this study, oxygen vacancies of reduced ceria and Pt/ or Rh/ceria are found to be the efficient and selective catalytic sites for NO reduction to N₂. Even at low concentrations, NO can compete with an excess of O₂ at 600 °C and a high GHSV of 170 000 L L⁻¹ h⁻¹, conditions in which SCR and NSR DeNO_x system are not able to function well. N₂O is not detected over the whole range of conditions, whereas NO₂ is only formed upon oxidation of the catalyst, after both NO and O₂ start to appear. For consideration of the fuel economy, the working temperature should be between 250 and 600 °C. Above 600 °C, most of the injected fuel was combusted with O₂. Below 250 °C, ceria support will not be reduced by fuel and the oxidation rate of the deposited carbon through oxygen from ceria lattice will be too low.

A quasi chemical vapor deposition method for the manufacture of well-defined covalent triazine framework (CTF) coatings on cordierite monoliths is reported. The resulting supported porous organic polymer is an excellent support for the immobilization of two different homogeneous catalysts: (1) an Ir^IIICp∗-based catalyst for the hydrogen production from formic acid and (2) a Pt^II-based catalyst for the direct activation of methane via Periana chemistry. The immobilized catalysts display a much higher activity in comparison with the unsupported CTF operated in slurry because of improved mass transport. Our results demonstrate that CTF-based catalysts can be further optimized by engineering at different length scales.

We tailored the size distribution of Pt nanoparticles (NPs) on graphene nanoplatelets at a given metal loading by using low-temperature atomic layer deposition carried out in a fluidized bed reactor operated at atmospheric pressure. The Pt NPs deposited at low temperature (100 °C) after 10 cycles were more active and stable towards the propene oxidation reaction than their high-temperature counterparts. Crucially, the gap in the catalytic performance was retained even after prolonged periods of time (>24 hours) at reaction temperatures as high as 450 °C. After exposure to such harsh conditions the Pt NPs deposited at 100 °C still retained a size distribution that is narrower than the one of the as-synthesized NPs obtained at 250 °C. The difference in performance correlated with the difference in the number of facet sites as estimated after the catalytic test. Our approach provides not only a viable route for the scalable synthesis of stable supported Pt NPs with tailored size distributions but also a tool for studying the structure-function relationship.

We studied the mechanism of NO reduction as well as its selectivity and reactivity in the presence of excess O₂. Results show that fuel injection and/or pretreatment are important for ceria catalyst reduction and carbon deposition on the catalyst surface. Oxygen defects of reduced ceria are the key sites for the reduction of NO into N₂. The deposited carbon acts as a buffer reductant, i.e., the oxidation of carbon by lattice oxygen recreates oxygen defects to extend the NO reduction time interval. A small amount of NO showed a full conversion into only N₂ both on the reduced Zr-La doped ceria and reduced Pt-Zr-La doped ceria. Only when the catalyst is oxidised NO is converted into NO₂.

The use of two different classes of covalent organic frameworks (covalent triazine and imine linked frameworks) as supports for molecular Ni²⁺ catalysts is presented. For COFs, a large concentration of N heteroatoms, either in the form of quasi bipyridine or as diiminopyridine moieties, allows for the coordination of NiBr₂ to the scaffold of the porous polymers. When applied as catalysts in the oligomerization of ethylene under mild reaction conditions (15 bar, 50 °C), these new catalysts display an activity comparable to those of their homogeneous counterpart and a fivefold higher selectivity to C₆ ⁺ olefins. Accumulation of long chain hydrocarbons within the porosity of the COFs leads to reversible deactivation. Full activity and selectivity of the best catalysts can be recovered upon washing with dichlorobenzene.

The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer-Tropsch synthesis (FTS) catalysts have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are re-engineered towards FTS catalysts by means of simple pyrolysis at 500 °C under a N₂ atmosphere and afterwards characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state. We discovered that the Fe loading (36-46 wt%) and nanoparticle size (3.6-6.8 nm) of the obtained catalysts are directly related to the elementary composition and porosity of the initial MOFs. Furthermore, the carbonization leads to similar surface areas for the C matrix (S_BET between 570 and 670 m² g^-1), whereas the pore width distribution is completely different for the various MOFs. The high catalytic performance (FTY in the range of 1.9-4.6 × 10^-4 mol_CO g_Fe ^-1 s^-1) of the resulting materials could be correlated to the Fe particle size and corresponding surface area, and only minor deactivation was found for the N-containing catalysts. Elemental analysis of the catalysts containing deliberately added promoters and inherent impurities from the commercial MOFs revealed the subtle interplay between Fe particle size and complex catalyst composition in order to obtain high activity and stability next to a low CH₄ selectivity.