Visualizing pore architecture and molecular transport boundaries in catalyst bodies with fluorescent nanoprobes

Multifunctional Strategies of Advanced Electrocatalysts for Efficient Urea Synthesis

The electrochemical reduction of nitrogenous species (such as N2, NO, NO2 -, and NO3 -) for urea synthesis under ambient conditions has been extensively studied due to their potential to realize carbon/nitrogen neutrality and mitigate environmental pollution, as well as provide a means to store renewable electricity generated from intermittent sources such as wind and solar power. However, the sluggish reaction kinetics and the scarcity of active sites on electrocatalysts have significantly hindered the advancement of their practical applications. Multifunctional engineering of electrocatalysts has been rationally designed and investigated to adjust their electronic structures, increase the density of active sites, and optimize the binding energies to enhance electrocatalytic performance. Here, surface engineering, defect engineering, doping engineering, and heterostructure engineering strategies for efficient nitrogen electro-reduction are comprehensively summarized. The role of each element in engineered electrocatalysts is elucidated at the atomic level, revealing the intrinsic active site, and understanding the relationship between atomic structure and catalytic performance. This review highlights the state-of-the-art progress of electrocatalytic reactions of waste nitrogenous species into urea. Moreover, this review outlines the challenges and opportunities for urea synthesis and aims to facilitate further research into the development of advanced electrocatalysts for a sustainable future.

Temperature-Programmed Desorption of Single Zeolite Nanoparticles

Zeolites are essential solid acid catalysts in various chemical processes. Temperature-programmed desorption (TPD) is one of the most established techniques used to characterize the acidity of zeolites by measuring the desorption kinetics of probes from bulk samples. However, conventional TPD can hardly deliver the intrinsic acid properties of zeolites because the apparent desorption kinetics are inevitably mixed with mass transfer and thermal conduction due to the large sample amount (∼0.1 g). Herein, we developed an optical microscopy approach to measure the TPD spectra of single zeolite nanoparticles, termed oTPD, by in situ monitoring of the reduced scattering intensity of individuals as a result of the desorption of probe molecules during heating. A significantly reduced sample amount contributed to the oTPD spectrum, revealing an intrinsic desorption temperature of ∼300 °C lower than the apparent value and also a greatly narrowed peak width from ∼150 to ∼15 °C. Correlating oTPD and micro-Raman spectra of the very same individuals further uncovered a linear dependence between the acidity and the content of silicon islands. This study provided unprecedented capabilities for measuring the intrinsic acid properties and the desorption kinetics of single zeolite nanoparticles, with implications for better understanding the structure-acidity relationship and for designing better zeolite catalysts.

Spatiotemporal Heterogeneity of Temperature and Catalytic Activation within Individual Catalyst Particles

Temperature is a critical parameter in chemical conversion, significantly affecting the reaction kinetics and thermodynamics. Measuring temperature inside catalyst particles of industrial interest (∼micrometers to millimeters), which is crucial for understanding the evolution of chemical dynamics at catalytic active sites during reaction and advancing catalyst designs, however, remains a big challenge. Here, we propose an approach combining two-photon confocal microscopy and state-of-the-art upconversion luminescence (UL) imaging to measure the spatiotemporal-resolved temperature within individual catalyst particles in the industrially significant methanol-to-hydrocarbons reaction. Specifically, catalyst particles containing zeolites and functional nanothermometers were fabricated using microfluidic chips. Our experimental results directly demonstrate that the zeolite density and particle size can alter the temperature distribution within a single catalyst particle. Importantly, the observed temperature heterogeneity plays a decisive role in the activation of the reaction intermediate and the utilization of active sites. We expect that this work opens a venue for unveiling the reaction mechanism and kinetics within industrial catalyst particles by considering temperature heterogeneity.

Unravelling potential reaction intermediates during catalytic pyrolysis of polypropylene with microscopy and spectroscopy

While plastics-to-plastics recycling via melting and re-extrusion is often the preferred option due to a relatively low CO2 footprint, this technique requires a highly sorted waste stream and plastic properties can often not be maintained. Obtaining aromatics, such as benzene, toluene, and xylene (BTX), via catalytic pyrolysis of polyolefins, such as polypropylene and polyethylene, offers another attractive recycling technology. In this process, a discarded crude oil refinery catalyst (ECAT) was previously shown to lower the unwanted formation of deactivating coke species compared to a fresh crude oil refinery catalyst (FCC-cat), while yielding 20 wt% aromatics from polypropylene. In this work, we study the underlying reaction mechanism for this chemical recycling process over the fresh and used refinery catalyst as well as a model system, not containing any zeolite material, using a combination of microscopy and spectroscopy. More specifically, by using in situ fluorescence microscopy, in situ infrared spectroscopy, in situ ultraviolet-visible spectroscopy as well as ex situ solid-state nuclear magnetic resonance, we observe highly fluorescent methylated aromatic intermediates that differ for the three catalyst materials under study both in their fluorescence, IR, UV-vis, and NMR spectroscopy features. This detailed micro-spectroscopic comparison informs which potential reaction intermediates lead to increased coke formation. Our results suggests that a next generation of catalyst materials for this process would profit from a higher accessibility and a milder acidity compared to an FCC-cat and shows the great potential of using ECAT to reduce coking and obtain a BTX stream, which could be become the chemical building blocks for the manufacturing of e.g., plastics and coating materials.

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.

Direct probing of single-molecule chemiluminescent reaction dynamics under catalytic conditions in solution

Chemical reaction kinetics can be evaluated by probing dynamic changes of chemical substrates or physical phenomena accompanied during the reaction process. Chemiluminescence, a light emitting exoenergetic process, involves random reaction positions and kinetics in solution that are typically characterized by ensemble measurements with nonnegligible average effects. Chemiluminescent reaction dynamics at the single-molecule level remains elusive. Here we report direct imaging of single-molecule chemiluminescent reactions in solution and probing of their reaction dynamics under catalytic conditions. Double-substrate Michaelis-Menten type of catalytic kinetics is found to govern the single-molecule reaction dynamics in solution, and a heterogeneity is found among different catalyst particles and different catalytic sites on a single particle. We further show that single-molecule chemiluminescence imaging can be used to evaluate the thermodynamics of the catalytic system, resolving activation energy at the single-particle level. Our work provides fundamental insights into chemiluminescent reactions and offers an efficient approach for evaluating catalysts.

Geometry and Chemistry: Influence of Pore Functionalization on Molecular Transport and Diffusion in Solvent-Filled Zirconium Metal-Organic Frameworks

Postsynthetic modification (PSM) of metal-organic frameworks (MOFs) enables incorporation of diverse functionalities in pores for chemical separations, drug delivery, and heterogeneous catalysis. However, the effect of PSM on molecular transport, which is essential for most applications of MOFs, has been rarely studied. In this paper, we used perfluoroalkane-functionalized Zr-MOF NU-1008 as a platform to systematically interrogate transport processes and mechanisms in solvated pores. We anchored perfluoroalkanes onto NU-1008 nodes by solvent-assisted ligand incorporation (SALI-n, with n = 3, 5, 7, and 9 denoting the number of fluorinated carbons). Transport of a luminescent molecule, BODIPY, through individual crystallites of four versions of methanol-filled SALI-n was monitored by confocal fluorescence microscopy as a function of time and location. In comparison with the parent NU-1008, the diffusivity of the probe molecules within SALI-n declined by 2- to 7-fold depending on chain length and loading, presumably due to the reduction in pore diameter or adsorptive interactions with perfluoroalkyl chains. Atomistic simulations were performed to uncover the microscopic behavior of the BODIPY diffusion in SALI-n. The perfluoroalkyl chains are observed to stay close to the pore walls, instead of extending toward the pore center. BODIPY molecules, which preferably interact with linkers, were pushed to the interior of the channels as the chain length increased, resulting in solvated diffusion and minor differences in the short-time mobility of BODIPY in SALI-n. This suggested that the observed decline of transport diffusivity in SALI-n mainly stemmed from the reduction in the pore size when these flexible chains are present. We anticipate that this proof of concept will assist in understanding how pore functionalization can physically and chemically affect mass transport in MOFs and will be useful in further guiding the design of PSM to realize the optimal performance of MOFs for various applications.

Operando Modeling of Zeolite-Catalyzed Reactions Using First-Principles Molecular Dynamics Simulations

Within this Perspective, we critically reflect on the role of first-principles molecular dynamics (MD) simulations in unraveling the catalytic function within zeolites under operating conditions. First-principles MD simulations refer to methods where the dynamics of the nuclei is followed in time by integrating the Newtonian equations of motion on a potential energy surface that is determined by solving the quantum-mechanical many-body problem for the electrons. Catalytic solids used in industrial applications show an intriguing high degree of complexity, with phenomena taking place at a broad range of length and time scales. Additionally, the state and function of a catalyst critically depend on the operating conditions, such as temperature, moisture, presence of water, etc. Herein we show by means of a series of exemplary cases how first-principles MD simulations are instrumental to unravel the catalyst complexity at the molecular scale. Examples show how the nature of reactive species at higher catalytic temperatures may drastically change compared to species at lower temperatures and how the nature of active sites may dynamically change upon exposure to water. To simulate rare events, first-principles MD simulations need to be used in combination with enhanced sampling techniques to efficiently sample low-probability regions of phase space. Using these techniques, it is shown how competitive pathways at operating conditions can be discovered and how broad transition state regions can be explored. Interestingly, such simulations can also be used to study hindered diffusion under operating conditions. The cases shown clearly illustrate how first-principles MD simulations reveal insights into the catalytic function at operating conditions, which could not be discovered using static or local approaches where only a few points are considered on the potential energy surface (PES). Despite these advantages, some major hurdles still exist to fully integrate first-principles MD methods in a standard computational catalytic workflow or to use the output of MD simulations as input for multiple length/time scale methods that aim to bridge to the reactor scale. First of all, methods are needed that allow us to evaluate the interatomic forces with quantum-mechanical accuracy, albeit at a much lower computational cost compared to currently used density functional theory (DFT) methods. The use of DFT limits the currently attainable length/time scales to hundreds of picoseconds and a few nanometers, which are much smaller than realistic catalyst particle dimensions and time scales encountered in the catalysis process. One solution could be to construct machine learning potentials (MLPs), where a numerical potential is derived from underlying quantum-mechanical data, which could be used in subsequent MD simulations. As such, much longer length and time scales could be reached; however, quite some research is still necessary to construct MLPs for the complex systems encountered in industrially used catalysts. Second, most currently used enhanced sampling techniques in catalysis make use of collective variables (CVs), which are mostly determined based on chemical intuition. To explore complex reactive networks with MD simulations, methods are needed that allow the automatic discovery of CVs or methods that do not rely on a priori definition of CVs. Recently, various data-driven methods have been proposed, which could be explored for complex catalytic systems. Lastly, first-principles MD methods are currently mostly used to investigate local reactive events. We hope that with the rise of data-driven methods and more efficient methods to describe the PES, first-principles MD methods will in the future also be able to describe longer length/time scale processes in catalysis. This might lead to a consistent dynamic description of all steps-diffusion, adsorption, and reaction-as they take place at the catalyst particle level.

Preparation and quantitative analysis of multicenter luminescence materials for sensing function

Luminescent sensing materials are attractive for environmental analysis due to their potential for high selectivity, excellent sensitivity and rapid (even instantaneous) response towards targeted analytes in diverse sample matrices. Many types of analytes have been detected in samples of wastewater for environmental protection, reagents and products in industrial production of drugs and pesticides, and biological markers in blood and urine for early diagnosis. It is still challenging, however, to develop appropriate materials with optimal sensing function for a targeted analyte. Here we synthesize metal-organic frameworks (MOFs) bearing multiple luminescent centers, such as metal cations (for example, Eu3+ and Tb3+), organic ligands and guests, which are chosen for optimal selectivity for the analytes of interest, including industrial synthetic intermediates and chiral drugs. Interaction between the metal node, ligand, guest and analyte results in a complex system with different luminescence properties compared with the porous MOF on its own. The operation time for the synthesis is usually less than 4 h; the quick screening for sensitivity and selectivity takes ~0.5 h and includes steps to optimize the energy levels and spectrum parameters. It can be used to accelerate the discovery of advanced sensing materials for practical applications.

Synergism between hierarchical MFI zeolites and alumina in alkene cross-metathesis reactions as a function of composition

Synergism between hierarchical zeolites and alumina in the preparation of active Mo catalysts, as a function of composition ratios, has been demonstrated in the cross-metathesis reaction between ethene and 2-butene. The metathesis reaction activity, reflected by ethene conversion, increases from 24.1% to 49.2% with the increase in the alumina content in composites from 10 wt% to 30 wt%. A further increase in the alumina content leads to the reduction in the metathesis activity, in which the ethene conversion decreases from 30.3% to 4.8% upon the enhanced alumina content from 50 wt% to 90 wt%. The impact of alumina content on the metathesis activity is closely associated with the interaction mode between the hierarchical ZSM-5 zeolite and alumina. TEM observation as well as EDS analysis and XPS results prove the progressive coating of alumina phase on the surface of zeolites along with the progressive enhancement of alumina content. The moderate alumina content in the composite enables the desired interaction between hierarchical zeolites and alumina, which is beneficial for the preparation of active catalysts for the alkene cross-metathesis reaction.

Addition of Pore-Forming Agents and Their Effect on the Pore Architecture and Catalytic Behavior of Shaped Zeolite-Based Catalyst Bodies

Porous materials, such as solid catalysts, are used in various chemical reactions in industry to produce chemicals, materials, and fuels. Understanding the interplay between pore architecture and catalytic behavior is of great importance for synthesizing a better industrial-grade catalyst material. In this study, we have investigated the modification of the pore architecture of zeolite-based alumina-bound shaped catalyst bodies via the addition of different starches as pore-forming agents. A combination of microscopy techniques allowed us to visualize the morphological changes induced and make a link between pore architecture, molecular transport, and catalytic performance. As for the catalytic performance in the methanol-to-hydrocarbons (MTH) reaction, pore-forming agents resulted in up to ∼12% higher conversion, an increase of 74% and 77% in yield (14% and 13% compared to 8.6% and 7.7% of the reference sample in absolute yields) toward ethylene and propylene, respectively, and an improved lifetime of the catalyst materials.

Targeting EGFR and Monitoring Tumorigenesis of Human Lung Cancer Cells In Vitro and In Vivo Using Nanodiamond-Conjugated Specific EGFR Antibody

Nanoprobes provide advantages for real-time monitoring of tumor markers and tumorigenesis during cancer progression and development. Epidermal growth factor receptor (EGFR) is a key protein that plays crucial roles for tumorigenesis and cancer therapy of lung cancers. Here, we show a carbon-based nanoprobe, nanodiamond (ND), which can be applied for targeting EGFR and monitoring tumorigenesis of human lung cancer cells in vitro and in vivo. The optimal fluorescent intensities of ND particles were observed in the human lung cancer cells and nude mice under in vivo imaging system. The fluorescence signal of ND particles can be real-time detected in the xenografted human lung tumor formation of nude mice. Moreover, the ND-conjugated specific EGFR antibody cetuximab (Cet) can track the location and distribution of EGFR proteins of lung cancer cells in vitro and in vivo. ND-Cet treatment increased cellular uptake ability of nanocomposites in the EGFR-expressed cells but not in the EGFR-negative lung cancer cells. Interestingly, single ND-Cet complex can be directly observed on the protein G bead by immunoprecipitation and confocal microscopy. Besides, the EGFR proteins were transported to lysosomes for degradation. Together, this study demonstrates that ND-conjugated Cet can apply for targeting EGFR and monitoring tumorigenesis during lung cancer progression and therapy.

Molecular transport in zeolite catalysts: depicting an integrated picture from macroscopic to microscopic scales

Increasing social sustainability triggers the persistent progress of industrial catalysis in energy transformation and chemical production. Zeolites have been demonstrated to be pivotal catalysts in chemical industries due to their moderate acidity and versatile well-defined pore structures. However, in the context of enhancing the performances of zeolite catalysts, the perspectives on the diffusion regulations within the pores and channels in the bulk phases or external surfaces of the zeolites are often overlooked. Establishing the structure-transport-reactivity relationships in heterogeneous catalysis can provide rational guidelines to design high-performance catalysts. Herein, this tutorial review attempts to systematically depict an integrated picture of molecular transport behaviors in zeolite catalysts from macroscopic to microscopic perspectives. The advances in the accurate diffusion measurements employing both macroscopic and microscopic techniques are briefly introduced. The diffusion characteristics in zeolite catalysts under working conditions (e.g., high temperature, multi-components, and reaction coupling) are then addressed. The macroscopic internal diffusion and the microscopic diffusion occurring in the micro-zones of zeolite crystals (e.g., surface diffusion, diffusion anisotropy, and confined diffusion) are reviewed and discussed in more detail. These diffusion behaviors highly impact the underlying reaction mechanism, catalytic performances, and catalyst optimization strategies. Finally, the multi-type pore systems of practical zeolite catalysts in industrial reactors and their transport behaviors are analyzed. The fully-crystalline monolithic zeolites in the absence of binders are highlighted as rising-star catalytic materials for industrial applications. The research challenges in this field and the potential future development directions are summarized.

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Zeolite chemistry and catalysis are expected to play a decisive role in the next decade(s) to build a more decentralized renewable feedstock-dependent sustainable society owing to the increased scrutiny over carbon emissions. Therefore, the lack of fundamental and mechanistic understanding of these processes is a critical "technical bottleneck" that must be eliminated to maximize economic value and minimize waste. We have identified, considering this objective, that the chemistry related to the first-generation reaction intermediates (i.e., carbocations, radicals, carbenes, ketenes, and carbanions) in zeolite chemistry and catalysis is highly underdeveloped or undervalued compared to other catalysis streams (e.g., homogeneous catalysis). This limitation can often be attributed to the technological restrictions to detect such "short-lived and highly reactive" intermediates at the interface (gas-solid/solid-liquid); however, the recent rise of sophisticated spectroscopic/analytical techniques (including under in situ/operando conditions) and modern data analysis methods collectively compete to unravel the impact of these organic intermediates. This comprehensive review summarizes the state-of-the-art first-generation organic reaction intermediates in zeolite chemistry and catalysis and evaluates their existing challenges and future prospects, to contribute significantly to the "circular carbon economy" initiatives.

Boosting propane dehydroaromatization by confining PtZn alloy nanoparticles within H-ZSM-5 crystals

A Pt–Zn@H-ZSM-5 catalyst with Pt–Zn alloy nanoparticles confined in H-ZSM-5 crystals exhibits a significantly improved performance in the propane dehydroaromatization reaction.

Altering Chain Flexibility of Aliphatic Polyesters for Yellow-Green Clusteroluminescence in 38 % Quantum Yield

Preparation of non-conjugated polymers with long-wavelength emission and high quantum yield (QY) is still a huge challenge. Herein, we report the first example of linear non-conjugated polyester exhibiting yellow-green clusteroluminescence (CL) and a high QY of 38 %. We discovered that the polyester P3 with balanced flexibility and rigidity showed the longest CL wavelength and highest QY. Systematically photophysical characterization unravel the key role of ester cluster in the CL and the cluster formation via the aggregate of ester units was visualized. Moreover, P3 was demonstrated to be a highly selective, quick-responsive (ca. 1.2 min) and sensitive detector (detection limit is 0.78 μM) for irons owing to the fast disassociation of clusters by irons. This work not only gains further mechanistic insight into CL but also provides a new strategy to design high-efficiency and long-wavelength CL, meanwhile, enlightens the glorious application prospect of luminescent polyester.

Stabilizing the framework of SAPO-34 zeolite toward long-term methanol-to-olefins conversion

As a commercial MTO catalyst, SAPO-34 zeolite exhibits excellent recyclability probably due to its intrinsic good hydrothermal stability. However, the structural dynamic changes of SAPO-34 catalyst induced by hydrocarbon pool (HP) species and the water formed during the MTO conversion as well as its long-term stability after continuous regenerations are rarely investigated and poorly understood. Herein, the dynamic changes of SAPO-34 framework during the MTO conversion were identified by 1D ²⁷Al, ³¹P MAS NMR, and 2D ³¹P-²⁷Al HETCOR NMR spectroscopy. The breakage of T-O-T bonds in SAPO-34 catalyst during long-term continuous regenerations in the MTO conversion could be efficiently suppressed by pre-coking. The combination of catalyst pre-coking and water co-feeding is established to be an efficient strategy to promote the catalytic efficiency and long-term stability of SAPO-34 catalysts in the commercial MTO processes, also sheds light on the development of other high stable zeolite catalyst in the commercial catalysis.

Stability of zeolite catalysts is a highly desirable property for commercial methanol to olefins conversion but extremely challenging to achieve. Here, the authors combine the catalyst pre-coking and water co-feeding to develop an efficient strategy to enhance the long-term stability of SAPO-34 catalyst.

Plastic Waste Conversion over a Refinery Waste Catalyst

Polypropylene (PP) makes up a large share of our plastic waste. We investigated the conversion of PP over the industrial Fluid Catalytic Cracking catalyst (FCC-cat) used to produce gasoline from crude oil fractions. We studied transport limitations arising from the larger size of polymers compared to the crude oil-based feedstock by testing the components of this catalyst separately. Infrared spectroscopy and confocal fluorescence microscopy revealed the role of the FCC matrix in aromatization, and the zeolite Y domains in coking. An equilibrium catalyst (ECAT), discarded during FCC operation as waste, produced the same aromatics content as a fresh FCC-cat, while coking decreased significantly, likely due to the reduced accessibility and activity of the zeolite domains and an enhanced cracking activity of the matrix due to metal deposits present in ECAT. This mechanistic understanding provides handles for further improving the catalyst composition towards higher aromatics selectivity.

Chemical Imaging of Hierarchical Porosity Formation within a Zeolite Crystal Visualized by Small-Angle X-Ray Scattering and In-Situ Fluorescence Microscopy

Introducing hierarchical porosity to zeolites is vital for providing molecular access to microporous domains. Yet, the dynamics of meso- and macropore formation has remained elusive and pore space ill-characterized by a lack of (in situ) microscopic tools sensitive to nanoporosity. Here, we probe hierarchical porosity formation within a zeolite ZSM-5 crystal in real-time by in situ fluorescence microscopy during desilication. In addition, we introduce small-angle X-ray scattering microscopy as novel characterization tool to map intracrystal meso- and macropore properties. It is shown that hierarchical porosity formation initiates at the crystal surface and propagates to the crystal core via a pore front with decreasing rate. Also, hierarchical porosity only establishes in specific (segments of) subunits which constitute ZSM-5. Such space-dependent meso- and macroporosity implies local discrepancies in diffusion, performance and deactivation behaviors even within a zeolite crystal.

Multimodal Imaging of Autofluorescent Sites Reveals Varied Chemical Speciation in SSZ-13 Crystals

A multimodal imaging study of chabazite is used to show the distribution of and discriminate between different emissive deposits arising as a result of the detemplation process. Confocal imaging, 3D fluorescence lifetime imaging, 3D multispectral fluorescence imaging, and Raman mapping are used to show three different types of emissive behaviours each characterised by different spatial distributions, trends in lifetime, spectral signals, and Raman signatures. A notable difference is seen in the morphology of agglomerated surface deposits and larger subsurface deposits, which experience lifetime augmentation due to spatial confinement. The distribution of organic residue throughout the crystal volume is comparable to XRF mapping that shows Si enrichment on the outer edges and higher Al content through the centre, demonstrating that a fluorescence-based technique can also be used to indirectly comment on the compositional chemistry of the inorganic framework.

Directed transforming of coke to active intermediates in methanol-to-olefins catalyst to boost light olefins selectivity

Methanol-to-olefins (MTO), the most important catalytic process producing ethylene and propylene from non-oil feedstocks (coal, natural gas, biomass, CO₂, etc.), is hindered by rapid catalyst deactivation due to coke deposition. Common practice to recover catalyst activity, i.e. removing coke via air combustion or steam gasification, unavoidably eliminates the active hydrocarbon pool species (HCPs) favoring light olefins formation. Density functional theory calculations and structured illumination microscopy reveal that naphthalenic cations, active HCPs enhancing ethylene production, are highly stable within SAPO-34 zeolites at high temperature. Here, we demonstrate a strategy of directly transforming coke to naphthalenic species in SAPO-34 zeolites via steam cracking. Fluidized bed reactor-regenerator pilot experiments show that an unexpectedly high light olefins selectivity of 85% is achieved in MTO reaction with 88% valuable CO and H₂ and negligible CO₂ as byproducts from regeneration under industrial-alike continuous operations. This strategy significantly boosts the economics and sustainability of MTO process.

Methanol-to-olefins is hindered by rapid catalyst deactivation due to coke deposition. Here the authors demonstrate an approach of directly transforming coke to active intermediates to simultaneously recover catalyst activity and boost light olefins selectivity.

Rethinking resolution estimation in fluorescence microscopy: from theoretical resolution criteria to super-resolution microscopy

Resolution is undoubtedly the most important parameter in optical microscopy by providing an estimation on the maximum resolving power of a certain optical microscope. For centuries, the resolution of an optical microscope is generally considered to be limited only by the numerical aperture of the optical system and the wavelength of light. However, since the invention and popularity of various advanced fluorescence microscopy techniques, especially super-resolution fluorescence microscopy, many new methods have been proposed for estimating the resolution, leading to confusions for researchers who need to quantify the resolution of their fluorescence microscopes. In this paper, we firstly summarize the early concepts and criteria for predicting the resolution limit of an ideal optical system. Then, we discuss some important influence factors that deteriorate the resolution of a certain fluorescence microscope. Finally, we provide methods and examples on how to measure the resolution of a fluorescence microscope from captured fluorescence images. This paper aims to answer as best as possible the theoretical and practical issues regarding the resolution estimation in fluorescence microscopy.

Implications of Biomolecular Corona for Molecular Imaging

The development of nanoparticle probes has opened up new possibilities for molecular imaging in the era of precision medicine. There are a wide range of nanoprobes that are being used for various modalities that have demonstrated promising potential in early detection, disease monitoring, and theranostics. However, the rate of successful clinical translation of the nanoprobes is very low and is affected by the lack of our understanding about nanoparticle interaction with biological fluids after systemic administration, thus representing an unmet clinical need. One of the poorly understood issues relates to the formation of biomolecular corona, a layer of biomolecules formed on the surface of nanoscale materials during their interactions with biological fluids. The biomolecular corona has several significant effects on the biodistribution of nanoprobes and their imaging ability by (i) reducing their targeting efficacy and (ii) affecting the intrinsic imaging properties (e.g., contrast capacity of magnetic nanoprobes). This review provides insights on the importance of considering biomolecular corona in the development of nanoprobes, which may enable their more efficient utilization for molecular imaging applications.

Control of Surface Barriers in Mass Transfer to Modulate Methanol-to-Olefins Reaction over SAPO-34 Zeolites

Mass transfer of guest molecules has a significant impact on the applications of nanoporous crystalline materials and particularly shape-selective catalysis over zeolites. Control of mass transfer to alter reaction over zeolites, however, remains an open challenge. Recent studies show that, in addition to intracrystalline diffusion, surface barriers represent another transport mechanism that may dominate the overall mass transport rate in zeolites. We demonstrate that the methanol-to-olefins (MTO) reaction can be modulated by regulating surface permeability in SAPO-34 zeolites with improved chemical liquid deposition and acid etching. Our results explicitly show that the reduction of surface barriers can prolong catalyst lifetime and promote light olefins selectivity, which opens a potential avenue for improving reaction performance by controlling the mass transport of guest molecules in zeolite catalysis.

Disentangling Reaction Processes of Zeolites within Single-Oriented Channels

Establishing structure-reactivity relationships for specific channel orientations of zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, a well-defined model system was developed to build structure-reactivity relationships for specific zeolite-channel orientations during various catalytic reaction processes, for example, the methanol- and ethanol-to-hydrocarbons (MTH and ETH) process as well as oligomerization reactions. The entrapped and effluent hydrocarbons from single-oriented zeolite ZSM-5 channels during the MTH process were monitored by using operando UV/Vis diffuse reflectance spectroscopy (DRS) and on-line mass spectrometry (MS), respectively. The results reveal that the straight channels favor the formation of internal coke, promoting the aromatic cycle. Furthermore, the sinusoidal channels produce aromatics, (e.g., toluene) that further grow into larger polyaromatics (e.g., graphitic coke) leading to deactivation of the zeolites. This underscores the importance of careful engineering of materials to suppress coke formation and tune product distribution by rational control of the location of zeolite acid sites and crystallographic orientations.

Imaging spatiotemporal evolution of molecules and active sites in zeolite catalyst during methanol-to-olefins reaction

Direct visualization of spatiotemporal evolution of molecules and active sites during chemical transformation in individual catalyst crystal will accelerate the intuitive understanding of heterogeneous catalysis. So far, widespread imaging techniques can only provide limited information either with large probe molecules or in model catalyst of large size, which are beyond the interests of industrial catalysis. Herein, we demonstrate a feasible deep data approach via synergy of multiscale reaction-diffusion simulation and super-resolution structured illumination microscopy to  illustrate the dynamical evolution of spatiotemporal distributions of gas molecules, carbonaceous species and acid sites in SAPO-34 zeolite crystals of several micrometers that are typically used in industrial methanol-to-olefins process. The profound insights into the inadequate utilization of activated acid sites and rapid deactivation are unveiled. The notable elucidation of molecular reaction-diffusion process  at the scale of single catalyst crystal via this approach opens an interesting method for mechanism study in materials synthesis and catalysis.