The refinery of the future.

Fossil fuels-coal, oil and gas-supply most of the world's energy and also form the basis of many products essential for everyday life. Their use is the largest contributor to the carbon dioxide emissions that drive global climate change, prompting joint efforts to find renewable alternatives that might enable a carbon-neutral society by as early as 2050. There are clear paths for renewable electricity to replace fossil-fuel-based energy, but the transport fuels and chemicals produced in oil refineries will still be needed. We can attempt to close the carbon cycle associated with their use by electrifying refinery processes and by changing the raw materials that go into a refinery from fossils fuels to carbon dioxide for making hydrocarbon fuels and to agricultural and municipal waste for making chemicals and polymers. We argue that, with sufficient long-term commitment and support, the science and technology for such a completely fossil-free refinery, delivering the products required after 2050 (less fuels, more chemicals), could be developed. This future refinery will require substantially larger areas and greater mineral resources than is the case at present and critically depends on the capacity to generate large amounts of renewable energy for hydrogen production and carbon dioxide capture.

Advancements in Assays for Micro- and Nanoplastic Detection: Paving the Way for Biomonitoring and Exposomics Studies.

Although plastic pollution and exposure to plastic-related compounds have received worldwide attention, health risks associated with micro- and nanoplastics (MNPs) are largely unknown. Emerging evidence suggests MNPs are present in human biofluids and tissue, including blood, breast milk, stool, lung tissue, and placenta; however, exposure assessment is limited and the extent of human exposure to MNPs is not well known. While there is a critical need to establish robust and scalable biomonitoring strategies to assess human exposure to MNPs and plastic-related chemicals, over 10,000 chemicals have been linked to plastic manufacturing with no existing standardized approaches to account for even a fraction of these exposures. This review provides an overview of the status of methods for measuring MNPs and associated plastic-related chemicals in humans, with a focus on approaches that could be adapted for population-wide biomonitoring and integration with biological response measures to develop hypotheses on potential health effects of plastic exposures. We also examine the exposure risks associated with the widespread use of chemical additives in plastics. Despite advancements in analytical techniques, there remains a pressing need for standardized measurement protocols and untargeted, high-throughput analysis methods to enable comprehensive MNP biomonitoring to identify key MNP exposures in human populations. This review aims to merge insights into the toxicological effects of MNPs and plastic additives with an evaluation of analytical challenges, advocating for enhanced research methods to fully assess, understand, and mitigate the public health implications of MNPs.

Surface-Activated Mechano-Catalysis for Ambient Conversion of Plastic Waste.

Improved recycling technologies can offer sustainable end-of-life options for plastic waste. While polyolefins can be converted into small hydrocarbons over acid catalysts at high temperatures, we demonstrate an alternative mechano-catalytic strategy at ambient conditions. The mechanism is fundamentally different from classical acidity-driven high-temperature approaches, exploiting mechanochemically generated radical intermediates. Surface activation of zirconia grinding spheres creates redox active surface sites directly at the point of mechanical energy input. This allows control over mechano-radical reactivity, while powder catalysts are not active. Optimized milling parameters enable the formation of 45% C1-10 hydrocarbons from polypropylene within 1 h at ambient temperature. While mechanochemical bond scission is undesired in plastic production, we show that it can also be exploited for chemical recycling.

Molecular Accessibility and Diffusion of Resorufin in Zeolite Crystals.

We have used confocal laser scanning microscopy on the small, fluorescent resorufin dye molecule to visualize molecular accessibility and diffusion in the hierarchical, anisotropic pore structure of large (~10 µm-sized) zeolite-ß crystals. The resorufin dye is widely used in life and materials science, but only in its deprotonated form because the protonated molecule is barely fluorescent in aqueous solution. In this work, we show that protonated resorufin is in fact strongly fluorescent when confined within zeolite micropores, thus enabling fluorescence microimaging experiments. We find that J-aggregation guest-guest interactions lead to a decrease in the measured fluorescence intensity that can be prevented by using non-fluorescent spacer molecules. We characterized the pore space by introducing resorufin from the outside solution and following its diffusion into zeolite-ß crystals. The eventual homogeneous distribution of resorufin molecules throughout the zeolite indicates a fully accessible pore network. This enables the quantification of the diffusion coefficient in the straight pores of zeolite-ß without the need for complex analysis, and we found a value of 3×10-15  m2  s-1 . Furthermore, we saw that diffusion through the straight pores of zeolite-ß is impeded when crossing the boundaries between zeolite subunits.

Molecular Accessibility and Diffusion of Resorufin in Zeolite Crystals.

Invited for the cover of this issue is the group of Professor Bert Weckhuysen at Utrecht University. The image depicts the change in fluorescence color of a resorufin dye molecule when it is protonated and confined inside the micropores of zeolite-ß. Read the full text of the article at 10.1002/chem.202302553.

Chitosan as Support Material for Metal-Organic Framework based Catalysts.

Turning waste into valuable products is one of the main challenges of the chemical industry. In this work, chitosan (CS), an abundant, low-cost, and non-toxic biopolymer derived from chitin, was reshaped into beads of ~3 mm. Their suitability as a support material for active phase catalyst materials was tested for a zirconium-based Metal-Organic Framework (MOF) with incorporated Pt, namely UiO-67-Pt. Its incorporation was investigated via two procedures: a one-pot synthesis (OPS) and a post-synthetic functionalization (PSF) synthesis method. Scanning electron microscopy (SEM) images show good UiO-67-Pt dispersion throughout the CS beads for the one-pot synthesized material (UiO-67-Pt-OPS@CS). However, this uniform dispersion was not observed for the post-synthetically functionalized material (UiO-67-Pt-PSF@CS). The success of the implementation of UiO-67-Pt was evaluated with ultraviolet-visible and infrared spectroscopy for both composite materials. Thermogravimetric analysis (TGA) reveals higher thermal stabilities for UiO-67-Pt-OPS@CS composite beads in comparison to pure CS beads, but not for UiO-67-Pt-PSF@CS. The study provides valuable insights into the potential of chitosan as a green, bead-shaped support material for MOFs, offering flexibility in their incorporation through different synthesis routes. It further contributes to the broader goal of the sustainable and eco-friendly design of a new generation of catalysts made from waste materials, which will be the topic of future studies.

Correction: Propane to olefins tandem catalysis: a selective route towards light olefins production.

Correction for 'Propane to olefins tandem catalysis: a selective route towards light olefins production' by Matteo Monai et al., Chem. Soc. Rev., 2021, 50, 11503-11529, https://doi.org/10.1039/D1CS00357G.

Da Vinci Project: Educating Sustainability Change-Makers with Transdisciplinary Challenge-Based Learning and Design Thinking.

Sustainability transitions need professionals with specific skills and attitudes that students often do not develop in their regular chemistry education. To foster sustainability change-maker competencies, we suggest augmenting higher education curricula, e.g., chemical degree programs, with transdisciplinary challenge-based learning combined with design thinking. The Da Vinci Project at Utrecht University (UU) in The Netherlands explores this approach, aiming to cultivate the undergraduates' sustainability change-maker competencies. After five years of experience, we reflected on the students' learning outcomes in this UU honors program. We conclude that transdisciplinary challenge-based education combined with design thinking provides unique opportunities for students to develop valuable skills and attitudes for navigating sustainability transitions, including the transition toward sustainable chemistry. These involve collaboration, communication, creative thinking, integrative problem-solving, stakeholder engagement, openness, empathy, the ability to deal with uncertainty and complexity, self-awareness, critical reflection, courage, and perseverance.

Visualizing the Structure, Composition and Activity of Single Catalyst Particles for Olefin Polymerization and Polyolefin Decomposition.

The structural and morphological characterization of individual catalyst particles for olefin polymerization, as well as for the reverse process of polyolefin decomposition, can provide an improved understanding for how these catalyst materials operate under relevant reaction conditions. In this review, we discuss an emerging analytical toolbox of 2D and 3D chemical imaging techniques that is suitable for investigating the chemistry and reactivity of related catalyst systems. While synchrotron-based X-ray microscopy still provides unparalleled spatial resolutions in 2D and 3D, a number of laboratory-based techniques, most notably focused ion beam-scanning electron microscopy, confocal fluorescence microscopy, infrared photoinduced force microscopy and laboratory-based X-ray nano-computed tomography, have helped to significantly expand the arsenal of analytical tools available to scientists in heterogeneous catalysis and polymer science. In terms of future research, the review outlines the role and impact of in situ and operando (spectro-)microscopy experiments, involving sophisticated reactors as well as online reactant and product analysis, to obtain real-time information on the formation, decomposition, and mobility of polymer phases within single catalyst particles. Furthermore, the potential of fluorescence microscopy, X-ray microscopy and optical microscopy is highlighted for the high-throughput characterization of olefin polymerization and polyolefin decomposition catalysts. By combining these chemical imaging techniques with, for example, chemical staining methodologies, selective probe molecules as well as particle sorting approaches, representative structure-activity relationships can be derived at the level of single catalyst particles.

Surface Carbon Formation and its Impact on Methane Dry Reforming Kinetics on Rhodium-Based Catalysts by Operando Raman Spectroscopy.

A mechanism for carbon deposition and its impact on the reaction kinetics of Methane Dry Reforming (MDR) using Rhodium-based catalysts is presented. By integrating Raman spectroscopy with kinetic analysis in an operando-annular chemical reactor under strict chemical conditions, we discovered that carbon deposition on a Rh/α-Al2O3 catalyst follows a nucleation-growth mechanism. The dynamics of carbon aggregates at the surface is found to be ruled by the CO2/CH4 ratio and the inlet CH4 concentration. The findings elucidate the spatiotemporal development of carbon aggregates on the catalyst surface and their effects on catalytic performance. Furthermore, the proposed mechanism for carbon formation shows that the influence of CO2 on MDR kinetics is an indirect result of carbon accumulation over time frames exceeding the turnover frequency, thus reconciling conflicting reports in the literature regarding CO2's kinetic role in MDR.

The Coking of a Solid Catalyst Rationalized with Combined Raman and Fluorescence Lifetime Microscopy.

The formation of carbon deposits is a major deactivation pathway for solid catalysts. Studying coking on industrially relevant catalysts is, however, often challenging due to the sample heterogeneity. That is especially true for zeolite-containing catalysts where fluorescence often hampers their characterization with Raman spectroscopy. We turned this disadvantage into an advantage and combined Raman and fluorescence (lifetime) microscopy to study the coking behavior of an equilibrium catalyst material used for fluid catalytic cracking of hydrocarbons. The results presented illustrate that this approach can yield new insights in the physicochemical processes occurring within zeolite-containing catalyst particles during their coking process. Ex situ analyses of single catalyst particles revealed considerable intra-sample heterogeneities. The sample-averaged Raman spectra showed a higher degree of graphitization when the sample was exposed to more hexane, while the sample-averaged fluorescence lifetime showed no significant trend. Simultaneous in situ Raman and fluorescence (lifetime) microscopy, used to follow the coking and the regeneration of single particles, gave more insights in the changing fluorescence dynamics. During the coking, the rise and decline of the average fluorescence lifetime suggested the prolonged presence of smaller coke species that are quenched more and more by adjacent larger polyaromatics acting as Förster-resonance-energy-transfer acceptors.

Highly Dispersed ZnO Sites in a ZnO/ZrO2 Catalyst Promote Carbon Dioxide-to-Methanol Conversion.

ZnO/ZrO2 catalysts have shown better activity in the CO2 hydrogenation to methanol compared with single component counterparts, but the interaction between ZnO and ZrO2 is still poorly understood. In particular, the effect of the ZrO2 support phase (tetragonal vs. monoclinic) was not systematically explored. Here, we have synthesized ZnO/ZrO2 catalysts supported on tetragonal ZrO2 (ZnO/ZrO2-t) and monoclinic ZrO2 (ZnO/ZrO2-m), which resulted in the formation of different ZnOx species, consisting of sub-nanometer ZnO moieties and large-sized ZnO particles, respectively. ZnO/ZrO2-t exhibited a higher methanol selectivity (81 vs. 39%) and methanol yield (1.25 vs. 0.67 mmol g-1 h-1) compared with ZnO/ZrO2-m. The difference in performance was attributed to the redox state and degree of dispersion of Zn, based on spectroscopy and microscopy results. ZnO/ZrO2-t had a high density of ZnOx-ZrOy sites, which favored the formation of active HCOO* species and enhanced the yield and selectivity of methanol along the formate pathway. Such ZnO clusters were further dispersed on ZrO2-t during catalysis, while larger ZnO particles on ZnO/ZrO2-m remained stable throughout the reaction. This study shows that the phase of ZrO2 supports can be used to control the dispersion of ZnO and the catalyst surface chemistry, and lead to enhanced catalytic performance.

Fluorescent-Probe Characterization for Pore-Space Mapping with Single-Particle Tracking.

Porous solids often contain complex pore networks with pores of various sizes. Tracking individual fluorescent probes as they diffuse through porous materials can be used to characterize pore networks at tens of nanometers resolution. However, understanding the motion behavior of fluorescent probes in confinement is crucial to reliably derive pore network properties. Here, we introduce well-defined lithography-made model pores developed to study probe behavior in confinement. We investigated the influence of probe-host interactions on diffusion and trapping of confined single-emitter quantum-dot probes. Using the pH-responsiveness of the probes, we were able to largely suppress trapping at the pore walls. This enabled us to define experimental conditions for mapping of the accessible pore space of a one-dimensional pore array as well as a real-life polymerization-catalyst-support particle.

Elucidating the Structure and Composition of Individual Bimetallic Nanoparticles in Supported Catalysts by Atom Probe Tomography.

Understanding and controlling the structure and composition of nanoparticles in supported metal catalysts are crucial to improve chemical processes. For this, atom probe tomography (APT) is a unique tool, as it allows for spatially resolved three-dimensional chemical imaging of materials with sub-nanometer resolution. However, thus far APT has not been applied for mesoporous oxide-supported metal catalyst materials, due to the size and number of pores resulting in sample fracture during experiments. To overcome these issues, we developed a high-pressure resin impregnation strategy and showcased the applicability to high-porous supported Pd-Ni-based catalyst materials, which are active in CO2 hydrogenation. Within the reconstructed volume of 3 × 105 nm3, we identified over 400 Pd-Ni clusters, with compositions ranging from 0 to 16 atom % Pd and a size distribution of 2.6 ± 1.6 nm. These results illustrate that APT is capable of quantitatively assessing the size, composition, and metal distribution for a large number of nanoparticles at the sub-nm scale in industrial catalysts. Furthermore, we showcase that metal segregation occurred predominately between nanoparticles, shedding light on the mechanism of metal segregation. We envision that the presented methodology expands the capabilities of APT to investigate porous functional nanomaterials, including but not limited to solid catalysts.

Tandem catalysis with double-shelled hollow spheres.

Metal-zeolite composites with metal (oxide) and acid sites are promising catalysts for integrating multiple reactions in tandem to produce a wide variety of wanted products without separating or purifying the intermediates. However, the conventional design of such materials often leads to uncontrolled and non-ideal spatial distributions of the metal inside/on the zeolites, limiting their catalytic performance. Here we demonstrate a simple strategy for synthesizing double-shelled, contiguous metal oxide@zeolite hollow spheres (denoted as MO@ZEO DSHSs) with controllable structural parameters and chemical compositions. This involves the self-assembly of zeolite nanocrystals onto the surface of metal ion-containing carbon spheres followed by calcination and zeolite growth steps. The step-by-step formation mechanism of the material is revealed using mainly in situ Raman spectroscopy and X-ray diffraction and ex situ electron microscopy. We demonstrate that it is due to this structure that an Fe2O3@H-ZSM-5 DSHSs-showcase catalyst exhibits superior performance compared with various conventionally structured Fe2O3-H-ZSM-5 catalysts in gasoline production by the Fischer-Tropsch synthesis. This work is expected to advance the rational synthesis and research of hierarchically hollow, core-shell, multifunctional catalyst materials.

Understanding the Reactivity of Supported Late Transition Metals on a Bare Anatase (101) Surface: A Periodic Conceptual DFT Investigation.

The rapidly growing interest for new heterogeneous catalytic systems providing high atomic efficiency along with high stability and reactivity triggered an impressive progress in the field of single-atom catalysis. Nevertheless, unravelling the factors governing the interaction strength between the support and the adsorbed metal atoms remains a major challenge. Based on periodic density functional theory (DFT) calculations, this paper provides insight into the adsorption of single late transition metals on a defect-free anatase surface. The obtained adsorption energies fluctuate, with the exception of Pd, between -3.11 and -3.80 eV and are indicative of a strong interaction. Depending on the considered transition metal, we could attribute the strength of this interaction with the support to i) an electron transfer towards anatase (Ru, Rh, Ni), ii) s-d orbital hybridisation effects (Pt), or iii) a synergistic effect between both factors (Fe, Co, Os, Ir). The driving forces behind the adsorption were also found to be strongly related to Klechkowsky's rule for orbital filling. In contrast, the deviating behaviour of Pd is most likely associated with the lower dissociation enthalpy of the Pd-O bond. Additionally, the reactivity of these systems was evaluated using the Fermi weighted density of states approach. The resulting softness values can be clearly related to the electron configuration of the catalytic systems as well as with the net charge on the transition metal. Finally, these indices were used to construct a model that predicts the adsorption strength of CO on these anatase-supported d-metal atoms. The values obtained from this regression model show, within a 95 % probability interval, a correlation of 84 % with the explicitly calculated CO adsorption energies.

Micro- and Nanoscale Heterogeneities in Zeolite Beta as Measured by Atom Probe Tomography and Confocal Fluorescence Microscopy.

Micro- and nanoscale information on the activating and deactivating coking behaviour of zeolite catalyst materials increases our current understanding of many industrially applied processes, such as the methanol-to-hydrocarbon (MTH) reaction. Atom probe tomography (APT) was used to reveal the link between framework and coke elemental distributions in 3D with sub-nanometre resolution. APT revealed 10-20 nanometre-sized Al-rich regions and short-range ordering (within nanometres) between Al atoms. With confocal fluorescence microscopy, it was found that the morphology of the zeolite crystal as well as the secondary mesoporous structures have a great effect on the microscale coke distribution throughout individual zeolite crystals over time. Additionally, a nanoscale heterogeneous distribution of carbon as residue from the MTH reaction was determined with carbon-rich areas of tens of nanometres within the zeolite crystals. Lastly, a short length-scale affinity between C and Al atoms, as revealed by APT, indicates the formation of carbon-containing molecules next to the acidic sites in the zeolite.

Carbon Deposit Analysis in Catalyst Deactivation, Regeneration, and Rejuvenation.

Hydrocarbon conversion catalysts suffer from deactivation by deposition or formation of carbon deposits. Carbon deposit formation is thermodynamically favored above 350 °C, even in some hydrogen-rich environments. We discuss four basic mechanisms: a carbenium-ion based mechanism taking place on acid sites of zeolites or bifunctional catalysts, a metal-induced formation of soft coke (i.e., oligomers of small olefins) on bifunctional catalysts, a radical-mediated mechanism in higher-temperature processes, and fast-growing carbon filament formation. Catalysts deactivate because carbon deposits block pores at different length scales, or directly block active sites. Some deactivated catalysts can be re-used, others can be regenerated or have to be discarded. Catalyst and process design can mitigate the effects of deactivation. New analytical tools allow for the direct observation (in some cases even under in situ or operando conditions) of the 3D-distribution of coke-type species as a function of catalyst structure and lifetime.

Advancing the Compositional Analysis of Olefin Polymerization Catalysts with High-Throughput Fluorescence Microscopy.

To optimize the performance of supported olefin polymerization catalysts, novel methodologies are required to evaluate the composition, structure, and morphology of both pristine and prepolymerized samples in a resource-efficient, high-throughput manner. Here, we report on a unique combination of laboratory-based confocal fluorescence microscopy and advanced image processing that allowed us to quantitatively assess support fragmentation in a large number of autofluorescent metallocene-based catalyst particles. Using this approach, significant inter- and intraparticle heterogeneities were detected and quantified in a representative number of prepolymerized catalyst particles (2D: ≥135, 3D: 40). The heterogeneity that was observed over several stages of slurry-phase ethylene polymerization (10 bar) is primarily attributed to the catalyst particles' diverse support structures and to the inhomogeneities in the metallocene distribution. From a mechanistic point of view, the 2D and 3D analyses revealed extensive contributions from a layer-by-layer fragmentation mechanism in synergy with a less pronounced sectioning mechanism. A significant number of catalyst particles were also found to display limited support fragmentation at the onset of the reaction (i.e., at lower polymer yields). This delay in activity or "dormancy" is believed to contribute to a broadening of the particle size distribution during the early stages of polymerization. 2D and 3D catalyst screening via confocal fluorescence microscopy represents an accessible and fast approach to characterize the structure of heterogeneous catalysts and assess the distribution of their fluorescent components and reaction products. The automation of both image segmentation and postprocessing with machine learning can yield a powerful diagnostic tool for future research as well as quality control on industrial catalysts.

Probing the Dynamics of Low-Overpotential CO2-to-CO Activation on Copper Electrodes with Time-Resolved Raman Spectroscopy.

Oxide-derived copper electrodes have displayed a boost in activity and selectivity toward valuable base chemicals in the electrochemical carbon dioxide reduction reaction (CO2RR), but the exact interplay between the dynamic restructuring of copper oxide electrodes and their activity and selectivity is not fully understood. In this work, we have utilized time-resolved surface-enhanced Raman spectroscopy (TR-SERS) to study the dynamic restructuring of the copper (oxide) electrode surface and the adsorption of reaction intermediates during cyclic voltammetry (CV) and pulsed electrolysis (PE). By coupling the electrochemical data to the spectral features in TR-SERS, we study the dynamic activation of and reactions on the electrode surface and find that CO2 is already activated to carbon monoxide (CO) during PE (10% Faradaic efficiency, 1% under static applied potential) at low overpotentials (-0.35 VRHE). PE at varying cathodic bias on different timescales revealed that stochastic CO is dominant directly after the cathodic bias onset, whereas no CO intermediates were observed after prolonged application of low overpotentials. An increase in cathodic bias (-0.55 VRHE) resulted in the formation of static adsorbed CO intermediates, while the overall contribution of stochastic CO decreased. We attribute the low-overpotential CO2-to-CO activation to a combination of selective Cu(111) facet exposure, partially oxidized surfaces during PE, and the formation of copper-carbonate-hydroxide complex intermediates during the anodic pulses. This work sheds light on the restructuring of oxide-derived copper electrodes and low-overpotential CO formation and highlights the power of the combination of electrochemistry and time-resolved vibrational spectroscopy to elucidate CO2RR mechanisms.