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Zeolites are one of the most successful catalyst materials of the 20th century and are anticipated to be crucial in the coming decades to transition towards a more sustainable and circular society. Traditional zeolite-based catalytic processes, such as hydrocarbon cracking and transalkylation involving fossil-based resources, are usually performed in the absence of water. With the development of renewable processes based on agricultural and municipal waste, oxygen-rich molecules must be converted, which involves the presence of water. Hence, the impact of water on zeolite-based catalytic performance becomes crucial. In this review, we discuss the current understanding of the role of water during zeolite catalysis and provide insights into mechanistic aspects of water–zeolite interactions. Special attention is paid to molecular modeling approaches. A synergy between experimental and theoretical approaches represents another major challenge in modern catalysis science as it provides routes towards the design of novel and more stable zeolite catalysts.

The methanol-to-hydrocarbons (MTH) process, commonly catalyzed by zeolites, is of great commercial interest and therefore widely studied both in industry and academia. However, zeolite-based catalyst materials are notoriously hard to study at the nano-scale. Atom probe tomography (APT) is uniquely positioned among the suite of characterization techniques, as it can provide 3D chemical information with sub-nm resolution. In this work, we have used APT to study the nano-scale coking behavior of zeolite SSZ-13 and its relation to bulk coke formation on the macro-/micro-scale studied with operando and in situ UV-vis spectroscopy and microscopy. Radial distribution function analysis (RDF) of the APT data revealed short carbon–carbon length scale affinities, consistent with the formation of larger aromatic molecules (coke species). Using nearest neighbor distribution (NND) analysis, an increase in the homogeneity of carbon was found with increasing time-on-stream. However, carbon clusters could not be isolated due to spatial noise and limited clustering. Therefore, it was found that the coke formation in zeolite SSZ-13 (CHA) is reasonably homogeneous on the nano-scale, and is rather similar to the silicoaluminophosphate analogue SAPO-34 (CHA) but different in nano-scale coking behavior compared to previously studied zeolite ZSM-5 (MFI).

In this review article, we discuss the latest advances and future perspectives of microfluidics for micro/nanoscale catalyst particle synthesis and analysis. In the first section, we present an overview of the different methods to synthesize catalysts making use of microfluidics and in the second section, we critically review catalyst particle characterization using microfluidics. The strengths and challenges of these approaches are highlighted with various showcases selected from the recent literature. In the third section, we give our opinion on the future perspectives of the combination of catalytic nanostructures and microfluidics. We anticipate that in the synthesis and analysis of individual catalyst particles, generation of higher throughput and better understanding of transport inside individual porous catalyst particles are some of the most important benefits of microfluidics for catalyst research.

The Fischer–Tropsch synthesis (FTS) reaction is one of the most promising processes to convert alternative energy sources, such as natural gas, coal or biomass, into liquid fuels and other high-value products. Despite its commercial implementation, we still lack fundamental insights into the various deactivation processes taking place during FTS. In this work, a combination of three methods for studying single catalyst particles at different length scales has been developed and applied to study the deactivation of Co/TiO2 Fischer–Tropsch synthesis (FTS) catalysts. By combining transmission X-ray microscopy (TXM), scanning transmission X-ray microscopy (STXM) and scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) we visualized changes in the structure, aggregate size and distribution of supported Co nanoparticles that occur during FTS. At the microscale, Co nanoparticle aggregates are transported over several μm leading to a more homogeneous Co distribution, while at the nanoscale Co forms a thin layer of ∼1–2 nm around the TiO2 support. The formation of the Co layer is the opposite case to the “classical” strong metal–support interaction (SMSI) in which TiO2 surrounds the Co, and is possibly related to the surface oxidation of Co metal nanoparticles in combination with coke formation. In other words, the observed migration and formation of a thin CoOx layer are similar to a previously discussed reaction-induced spreading of metal oxides across a TiO2 surface.

A study on the influence of H2 and the degree of titanation of a Cr/SiO2 Phillips polymerisation catalyst on the selective oligomerisation of ethylene induced by pre-contacting the catalyst with triethylaluminium (TEAl) is presented. Ethylene oligomerisation reactions were performed at 373 K and 1 bar, inside a quartz reactor of a specially designed operando experimental setup, which allowed examination of the catalysts by UV-vis-NIR diffuse reflectance spectroscopy, while the gas phase was continuously monitored by on-line mass spectroscopy and subsequently analysed by gas chromatography. With this combination of techniques, it was possible to acquire detailed insight into the different distributions of produced oligomers, which were highly dependent on the catalyst structure. The addition of small amounts of Ti significantly changes the electronic environment of Cr oligomerisation sites by the formation of Cr–O–Ti–O–Si linkages, favouring β-H transfer and increasing the selectivity towards butene at the expense of 1-hexene. Moreover, we show that ethylene oligo-/polymerisation reactions follow at least two different pathways, i.e. metallacycle for olefinic species with a broken Schulz-Flory distribution, and Cossee–Arlman for other hydrocarbon species.

A series of fluorescent probe molecules based on the commercially available trans-4-(4-(diethylamino)styryl)-N-methylpyridinium iodide (DAMPI) scaffold has been developed. The dynamic radii of these DAMPI-type probes covered a range of 5.8 to 10.1 Å and could be changed by varying the alkyl substituents on the amine donor group, with limited effect on the electronic properties. These probe molecules allow for the direct evaluation of the molecular accessibility into confined spaces, more specifically the micropore architecture of zeolite materials. Evaluation of industrially relevant zeolite materials with 8- (CHA), 10- (MFI) and 12-membered ring pores (FAU) showed that steric bulk influences the rate of adsorption, the amount of probe molecule taken up by the zeolite as well as the interaction of the probe molecule with the zeolite material. Furthermore, a positive linear correlation is found between the pore–probe size difference and total probe uptake by the zeolite. The absorption spectra of each probe molecule within the zeolites show that this DAMPI-type compound is chemically bound to the zeolite's acid sites. The new approach shows the general principle of determining size-accessibility relationships in microporous solids with a series of fluorescent probes of systematically tunable size.

Au-Ti-SBA-15 catalysts have been synthesized using different preparation routes. Ti-SBA-15 supports with Si/Ti ratio ranging from 10 to 80 have been prepared by grafting and direct synthesis. X-ray fluorescence (XRF), X-ray diffraction (XRD), diffuse reflectance UV-visible spectroscopy (DRS), transmission electron microscopy (TEM) and nitrogen sorption were applied for the characterization of the prepared catalysts. The catalytic activities of the Au/Ti-SBA-15 materials have been investigated in the direct epoxidation of propene by using a mixture of H2 and O2 and its performance was compared with an Au/TiO2 catalyst. The activity results were then interpreted with reference to the characterization.

Aspuru-Guzik, Alán et al., To mark the occasion of Nature Chemistry turning 10 years old, we asked scientists working in different areas of chemistry to tell us what they thought the most exciting, interesting or challenging aspects related to the development of their main field of research will be — here is what they said.