With the growing importance of developing new and improved methodologies for plastic recycling, conducting reproducible research and ensuring that results are transferable across labs are increasingly important. This Voices article reflects on how academia and industry view the path forward for strengthening reproducibility to advance science and enable a circular plastics economy.

Understanding the kinetics and mechanism of deactivation process favors the design of more effective strategies to improve catalyst function. We herein investigate the deactivation mechanism of Cr-MIL-101 catalyst during aqueous-phase glucose isomerization and epimerization. The study on effects of synthesis protocols and post-activation excludes the possibility of mass-transfer limitation in confined nanocage as the origin of limited catalytic activity. Contrary to the previous observation, the isotopic-tracer and NMR spectroscopy demonstrates that the formation of mannose proceeds by two mechanisms, i.e., the intramolecular 1, 2-carbon shift and two-step isomerization. Thermodynamic profiling reveals that Cr-MIL-101-catalyzed aqueous-phase glucose transformation exhibits a low intrinsic activity and deactivation phenomenon. Theoretical calculations confirm the non-selective nature of trinuclear chromium (III) clusters within the framework architecture, which demonstrate comparable adsorption affinities toward hexoses (glucose, fructose, and mannose). Additionally, the residual terephthalic acids, solvent water, and certain by-products can bind to the Cr sites, indicating that catalyst deactivation is primarily due to Cr-site-blocking. Based on these findings, a set of generalized phenomenological kinetic and deactivation kinetics models capturing the most relevant features of deactivation were developed and validated by experimental dataset. These models quantitatively describe the kinetic and deactivation behaviors, explicitly accounting for the underlying mechanism of competitive binding. Eventually, kinetic parameters derived from model regression analysis are discussed in relation to the underlying reaction pathways. The potential strategies to enhance intrinsic catalytic activity and mitigate catalyst deactivation are proposed.

The ability to quantitatively compare newly evolving catalytic materials and technologies is hindered by the widespread availability of catalytic data collected in a consistent manner. While certain catalytic chemistries have been widely studied across decades of scientific research, the ability to quantitatively utilize the available literature information is hindered by variability in reaction conditions, types of reported data, and reporting procedures. Here, we present CatTestHub, a database dedicated to providing benchmarking experimental data for heterogeneous catalysis. Through the selection of probe chemistries, combined with material characterization information and the systematic reporting of kinetic information, the database provides a collection of information that provides a collection of catalytic benchmarks for distinct classes of active sites. We propose that this online and open-access platform could serve as a community wide benchmark, the quality of which is improved through continuous addition of kinetic information on select catalytic systems by members of the heterogeneous catalysis community at large. In this initial iteration, we present benchmarking data relevant to the decomposition of methanol and formic acid over metal surfaces, as well as the Hofmann elimination of alkylamines over aluminosilicate zeolites. Details of the database, the logic of its construction, and the means through which to navigate are presented here, along with examples of catalytic insights readily drawn from the available information.

Chemical upcycling of polyethylene (PE) to long-chain alkylaromatics through tandem hydrocracking/aromatization has potential to provide value-added chemicals. However, the liquid product is a complex mixture of alkanes, alkylbenzenes, and polyaromatics, limiting its direct usability. The most valuable component of the product mixture is the alkylbenzenes because of their potential as precursors to anionic surfactants. In this study, a one-pot reactive separation is described. Sulfonating the product mixture from PE upcycling with silica sulfuric acid followed by neutralization with sodium hydroxide yields sodium alkylbenzenesulfonates (up to 93 mol % selectivity), along with a separate phase of lubricant-range hydrocarbons as a coproduct. Compared to petroleum-based sodium dodecylbenzenesulfonates, the reported PE-derived surfactant molecules show competitive physicochemical properties, including surface tension and interfacial tension. According to life cycle assessment, the described reaction strategy demonstrates 20% lower greenhouse gas emissions, when considering uses for the coproducts of PE upcycling, compared to conventional linear alkylbenzenesulfonates (LAS) manufacturing directly from petrochemical feedstocks.

The extent of charge transfer between adsorbed reactants and a catalyst surface plays a key role in determining binding energy and catalytic activity. Here, we describe the technique of ‘isopotential titration’ (IPT) to quantify the magnitude and direction of charge transfer between adsorbates and catalytic surfaces. The method used a ‘catalytic condenser’ device (Pt/C/70 nm HfO2/p++-Si) to evaluate the adsorption of hydrogen on a platinum-on-carbon conductive surface on a HfO2 (70 nm) film on a silicon wafer, with a potentiostat applying fixed (zero) voltage between the conductive Pt/C and silicon wafer layers. Dissociative adsorption of hydrogen on Pt resulted in electron flow through the external circuit from the Pt electrode toward the Si substrate, indicating that adsorbed hydrogen atoms donated electron density to the Pt surface, which then equilibrated with electrons flowing through the potentiostat to the silicon substrate. Desorption of hydrogen from the Pt surface exhibited equal and opposite current flow. The magnitude of the measured charge transfer upon hydrogen adsorption increased with increasing temperature from 100 to 200 °C, consistent with a larger change in H surface coverage at higher temperatures for cycling gaseous H2 partial pressures between 0.5% and 99.999%. Charge transferred from H atoms to the Pt was estimated as 0.17% of an electron donated per adsorbed H atom. The extent of charge transfer was comparable with a computed Bader charge analysis, which calculated an average of 0.4% of an electron transferred from adsorbing H to Pt at high surface coverage. With hydrogen adsorption being an example, isopotential titrations provide a new tool to quantify charge transfer events in heterogeneous catalytic systems.

For programmable catalysis applications, nanolaminates composed of thin alternating layers of alumina and titania (ATO) were engineered using atomic layer deposition (ALD) as the dielectric material for a Pt-on-carbon catalytic condenser. Systematic investigation assessed synthesis parameters such as deposition temperature, alumina and titania layer thicknesses, the total number of layers (and interfaces), and the presence of a capping alumina layer on the maximum achievable charge accumulation in the Pt catalyst layer. The highest capacitance ATO configuration demonstrated a specific capacitance of ~1,200 nF/cm2 with working voltages of ±5 V, enabling the storage of 4×10^13 electrons or holes per cm2 at room temperature. Adsorption of carbon monoxide on the Pt/C-ATO device characterized by grazing incidence infrared spectroscopy showed changes in the surface binding energy of 13.1 ± 0.8 kJ/mol for an applied external voltage bias of ±1 V. The results enhance our understanding of nanolaminate structures and provide a method for increasing charge condensation strength for higher temperature surface chemistries.

Supported platinum nanoparticle catalysts are known to convert polyolefins to high-quality liquid hydrocarbons using hydrogen under relatively mild conditions. To date, few studies using platinum grafted onto various metal oxide (M x O y ) supports have been undertaken to understand the role of the acidity of the oxide support in the carbon-carbon bond cleavage of polyethylene under consistent catalytic conditions. Specifically, two Pt/MxOy catalysts (MxOy = SrTiO3 and SiO2-Al(2)O3; Al = 3.0 wt %, target Pt loading 2 wt % Pt similar to 1.5 nm), under identical catalytic polyethylene hydrogenolysis conditions (T = 300 degree celsius, P(H2) = 170 psi, t = 24 h; M-w = similar to 3,800 g/mol, M-n = similar to 1,100 g/mol, D = 3.45, N-branch/100C = 1.0), yielded a narrow distribution of hydrocarbons with molecular weights in the range of lubricants (M-w = < 600 g/mol; M-n < 400 g/mol; D = 1.5). While Pt/SrTiO3 formed saturated hydrocarbons with negligible branching, Pt/SiO2-Al2O3 formed partially unsaturated hydrocarbons (<1 mol % alkenes and similar to 4 mol % alkyl aromatics) with increased branch density (N-branch/100C = 5.5). Further investigations suggest evidence for a competitive hydrocracking mechanism occurring alongside hydrogenolysis, stemming from the increased acidity of Pt/SiO2-Al2O3 compared to Pt/SrTiO3. Additionally, the products of these polymer deconstruction reactions were found to be independent of the polyethylene feedstock, allowing the potential to upcycle polyethylenes with various properties into a value-added product.

Atomically dispersed first-row transition metals embedded in nitrogen-doped carbon materials (M-N-C) show promising performance in catalytic hydrogenation but are less well-studied for reactions with more complex mechanisms, such as hydrogenolysis. Their ability to catalyze selective C-O bond cleavage of oxygenated hydrocarbons such as aryl alcohols and ethers is enhanced with the participation of ligands directly bound to the metal ion as well as longer-range contributions from the support. In this article, we describe how Fe-N-C catalysts with well-defined local structures for the Fe sites catalyze C-O bond hydrogenolysis. The reaction is facilitated by the N-C support. According to spectroscopic analyses, the as-synthesized catalysts contain mostly pentacoordinated FeIII sites, with four in-plane nitrogen donor ligands and one axial hydroxyl ligand. In the presence of 20 bar of H2 at 170-230 °C, the hydroxyl ligand is lost when N4FeIIIOH is reduced to N4FeII, assisted by the H2 chemisorbed on the support. When an alcohol binds to the tetracoordinated FeII sites, homolytic cleavage of the O-H bond is accompanied by reoxidation to FeIII and H atom transfer to the support. The role of the N-C support in catalytic hydrogenolysis is analogous to the behavior of chemically and redox-non-innocent ligands in molecular catalysts based on first-row transition metal ions and enhances the ability of M-N-Cs to achieve the types of multistep activations of strong bonds needed to upgrade renewable and recycled feedstocks.

This paper investigates parameter estimation of rate constants appearing in chemical mechanisms. As most chemical mechanisms are more complex than can be supported by available laboratory measurements, model reduction is a required first step. The quasisteady-state assumption and the reaction equilibrium assumption are presented as the two main model reduction methods. Reliable quantification of the approximate confidence intervals of the estimated parameters is a second key step. A brief overview of current numerical software for this purpose is provided. Parameter estimation with a starting mechanism and typically available simulated laboratory measurements is then applied to three illustrative example systems: (i) an electrochemical oxygen reduction reaction, (ii) butene isomerization by a metathesis mechanism, and (iii) enzymatic kinetics taking place in bacterial microcompartments. The reliability of the model reduction techniques and the current computational software is assessed based on the outcomes of these three example chemistries. In all three examples, the quasisteady-state assumption was required to remove some large rate constants governing low concentration, highly reactive species that could not be measured. After the model reduction, the parameter confidence intervals were then used to determine what extra measurements were required to identify the model, or the model was reparameterized to obtain an identifiable reduced set of parameters for the given measurements.

CO2 has attracted much attention as a C-1 feedstock for synthetic fuels via its selective catalytic hydrogenation to liquid hydrocarbons. One strategy is the catalytic reduction of CO2 to CO through the reverse water-gas shift (RWGS) reaction, followed by the hydrogenation of CO. In this work, potassium tris(tert-butoxy)ferrate, [{(THF)(2)KFe(OtBu)(3)}(2)], was supported on alumina that had been partially dehydroxylated at 500 degrees C (Al2O3-500), and the resulting catalyst was investigated in the selective reduction of CO2 to CO. The active site precursor was identified as [(THF)K(AlsO)Fe(OtBu)(2)(OHAl)] (i.e., [(THF)KFe(OtBu)(2)]/Al2O3-500), denoted 2-K, based on elemental analysis, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (high-resolution transmission electron microscopy (HRTEM) and EDS), X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Under the reaction conditions, the precursor becomes an active, stable, and selective RWGS catalyst (100% selectivity to CO at 22.5% CO2 conversion). The reaction mechanism was studied by operando DRIFT spectroscopy and density functional theory (DFT) modeling. The results are consistent with a mechanism involving H-2 activation by K[(AlsO)(2)FeOH], leading to K[(AlsO)(2)FeH]. CO2 insertion gives hydroxycarbonyl intermediate K[(AlsO)(2)FeCOOH], followed by liberation of CO to regenerate K[(AlsO)(2)FeOH].

Ga ions dispersed on alumina catalyze propane dehydrogenation (PDH). Their reactivity has been attributed to the presence of isolated Ga sites, while aggregation to GaOx oligomers and reduction to Ga-I are reported to be responsible for catalyst deactivation. In this study, we present the preparation and characterization of a highly active and stable single-site catalyst for propane dehydrogenation, consisting of fully dispersed Ga-III ions on gamma-alumina. The catalyst was synthesized using a surface organometallic chemistry route. Grafting [Ga(OtBu)(3)](2) onto Al2O3-500 results in the formation of monopodal [(AlsO)Ga(OtBu)(2)] (I). The controlled thermal treatment of (I) at 300 degrees C removes the alkoxide ligands and converts (I) into tetracoordinated [(AlsO)(3)Ga(AlsO-X), X = Al-s or H] (II). The structures of the intermediate species (I) and the active species (II) were confirmed through elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid-state NMR, and X-ray absorption spectroscopy (XAS). Material (II) was tested in PDH at 540 degrees C and exhibited high activity and stability compared to its silica-supported counterpart [(equivalent to SiO)(3)Ga], suggesting that the isolated nature and robust attachment of (II) onto gamma-alumina limit its deactivation.

The large production volumes of commodity polyolefins (specifically, polyethylene, polypropylene, polystyrene, and poly(vinyl chloride)), in conjunction with their low unit values and multitude of short-term uses, have resulted in a significant and pressing waste management challenge. Only a small fraction of these polyolefins is currently mechanically recycled, with the rest being incinerated, accumulating in landfills, or leaking into the natural environment. Since polyolefins are energy-rich materials, there is considerable interest in recouping some of their chemical value while simultaneously motivating more responsible end-of-life management. An emerging strategy is catalytic depolymerization, in which a portion of the C-C bonds in the polyolefin backbone is broken with the assistance of a catalyst and, in some cases, additional small molecule reagents. When the products are small molecules or materials with higher value in their own right, or as chemical feedstocks, the process is called upcycling. This review summarizes recent progress for four major catalytic upcycling strategies: hydrogenolysis, (hydro)cracking, tandem processes involving metathesis, and selective oxidation. Key considerations include macromolecular reaction mechanisms relative to small molecule mechanisms, catalyst design for macromolecular transformations, and the effect of process conditions on product selectivity. Metrics for describing polyolefin upcycling are critically evaluated, and an outlook for future advances is described.

Rational catalyst design and optimal solvent selection are key to advancing biorefining. Here, we explored the organocatalytic isomerization of D-fructose to a valuable rare monosaccharide, D-allulose, as a function of solvent. The isomerization of D-fructose to D-allulose competes with its isomerization to D-glucose and sugar degradation. In both water and DMF, the catalytic activity of amines towards D-fructose is correlated with their basicity. Solvents impact the selectivity significantly by altering the tautomeric distribution of D-fructose. Our results suggest that the furanose tautomer of D-fructose is isomerized to D-allulose, and the fractional abundance of this tautomer increases as follows: water < MeOH < DMF approximate to DMSO. Reaction rates are also higher in aprotic than in protic solvents. The best D-allulose yield, 14 %, was obtained in DMF with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. The reaction kinetics and mechanism were explored using operando NMR spectroscopy. (c) 2022 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Gallium-based heterogeneous catalysts originally developed for commercial use in propane dehydroaromatization have been explored extensively as potential replacements for Pt- and Cr-based catalysts used in propane dehydrogenation for on-demand propylene production. In a large number of experimental and theoretical studies, active sites with a variety of Ga nuclearities, coordination environments, and oxidation states have been proposed. Isolated Ga(I) ions are often invoked, despite the scarcity of well-defined molecular species and their well-documented instability. In this study, we investigate the appearance of a high-intensity, low-energy white line at the Ga K-edge upon reduction of Ga/HZSM-5 by H2 at a temperature of ca. 500 degrees C, accompanied by a dramatic reduction in the Ga/gamma-Al2O3 does not show such behavior. In order to lay a rigorous foundation for characterizing these types of systems and to establish experimental signatures for the elusive Ga(I) oxidation state, we recorded Ga K-edge X-ray absorption spectra [including high-energy-resolution fluorescence detection-X-ray absorption near-edge spectroscopy (HERFD-XANES)] for several well-defined molecular and crystalline Ga(I) compounds. XANES is essential to establishing the presence of Ga(I), despite the overlap in edge energies with organoGa(III) compounds, because Ga(I)-containing oxide materials show very weak EXAFS scattering. Compared to the XANES of trigonal Ga(III)-containing materials, Ga(I) spectra display a significantly more intense white line feature. Theoretical simulations agree well with this experimental observation and reveal that the strong XANES intensity originates from the superposition of transitions to several empty, nearly degenerate p-like states. These signatures provide compelling evidence for assigning the intense white line and dramatic loss of EXAFS intensity in Ga/HZSM-5 to the near-quantitative reduction of Ga(III) to Ga(I), while the weaker white line and conventional EXAFS signal of Ga/gamma-Al2O3 point to, at most, a minor fraction of Ga(I) sites.

The active site speciation of phosphorus-containing all-silica zeolites, P-zeosils, involves a dynamic distribution that is manipulated through controlled hydrolysis of the catalytic material. While water vapor is known to enhance the catalytic activity of phosphorus-based catalysts through phosphorous linkage hydrolysis, here we demonstrate that hydrolysis using a combination of water and sufficiently basic nitrogen-containing compounds like alkylamines increases the acid site density by more than an order of magnitude relative to water-only hydrolysis. The approach of base-assisted hydrolysis was found to be applicable to multiple catalytic chemistries, facilitating both the rates of alcohol dehydration (300× rate enhancement) and alkylamine Hofmann elimination (15× rate enhancement) over P-zeosils. Through a broad array of in situ and ex situ characterization, the enhancement of catalytic activity via base-facilitated hydrolysis was attributed to enhanced acid site density as a result of shifting the dynamic distribution of P-moieties to less condensed states. Specifically, more recalcitrant P-O-P linkages not cleaved through water only hydrolysis, were readily hydrolyzed in the presence of a base. Sufficient basicity in the nitrogen-containing group is critical to access the highest possible density of acid sites, which greatly exceeds that achievable through hydrolysis alone.

Catalytic conversion of waste polyolefins to value-added alkylaromatics could contribute to carbon recycling. Compared with tandem hydrogenolysis/aromatization of polyethylene (PE) catalyzed by Pt/ g-Al2O3 at 280 degrees C, both a 5-fold enhancement in the rate of C-C bond scission and a doubling of the molar yield of alkylaromatics were achieved using a more acidic Pt/F-Al2O3 catalyst instead. Bifunctional (metal/acid) catalysts also generate alkylaromatic products with lower average carbon numbers (ca. C20), similar to conventional anionic surfactants. Because physical mixtures of weakly acidic Pt/ g-Al2O3 or non-acidic Pt/SiO2 with strongly Bronsted acidic Cl-Al2O3 or F-Al2O3 are also effective, the tandem reaction does not require nanoscale intimacy between metal and acid active sites. Kinetic studies using triacontane (norm-C30H62) as a model for PE show that the Pt-catalyzed dehydrogenation/hydrogenation reactions are quasi-equilibrated, while the acid-catalyzed C-C bond scission and skeletal transformations (isomerization and cyclization) determine the overall rates of depolymerization and aromatic formation.

Depolymerization and upcycling are promising approaches to managing plastic waste. However, quantitative measurements of reaction rates and analyses of complex product mixtures arising from depolymerization of polyolefins constitute significant challenges in this emerging field. Here, we detail techniques for recovery and analysis of products arising from batch depolymerization of polyethylene. We also describe quantitative analyses of reaction rates and products selectivity. This protocol can be extended to depolymerization of other plastics and characterization of other product mixtures including long-chain olefins. For complete details on the use and execution of this protocol, please refer to Sun et al.1.

The effect of catalyst hydrophobicity on the kinetics of hydrogenation of aqueous phenol was investigated. The hydrophobicity of a Pd/SBA-15 catalyst was altered by synthesizing an organosilane with biphenylene framework linkers. Partitioning of phenol between the aqueous solution and the pores favors the hydrophobic catalyst by an order of magnitude at room temperature, relative to the hydrophilic catalyst. The rate of hydrogenation at 75 °C is higher in the hydrophobic catalyst, as is the selectivity for the partial hydrogenation product, cyclohexanone. Analysis of kinetic profiles measured using operando 13 C NMR reveals that the hydrophobic catalyst has a larger apparent (i.e., composite) adsorption constant for phenol, which results in higher phenol surface coverage and, consequently, faster and more selective hydrogenation to cyclohexanone.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTTo Err is Human; To Reproduce Takes TimeSusannah L. Scott*Susannah L. Scott*Email: [email protected]More by Susannah L. Scotthttps://orcid.org/0000-0003-1161-0499, T. Brent GunnoeT. Brent GunnoeMore by T. Brent Gunnoehttps://orcid.org/0000-0001-5714-3887, Paolo FornasieroPaolo FornasieroMore by Paolo Fornasierohttps://orcid.org/0000-0003-1082-9157, and Cathleen M. CruddenCathleen M. CruddenMore by Cathleen M. Cruddenhttps://orcid.org/0000-0003-2154-8107Cite this: ACS Catal. 2022, 12, 6, 3644–3650Publication Date (Web):March 9, 2022Publication History Published online9 March 2022Published inissue 18 March 2022https://pubs.acs.org/doi/10.1021/acscatal.2c00967https://doi.org/10.1021/acscatal.2c00967editorialACS PublicationsCopyright © 2022 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views13463Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (768 KB) Get e-Alertsclose Get e-Alerts