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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO 2 Reduction

Here, copper electrodes, prepared by reduction of oxidized metallic copper, have been reported to exhibit higher activity for the electrochemical reduction of CO 2 and better selectivity toward C 2 and C 3 (C 2+ ) products than metallic copper that has not been preoxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO 2 reduction, with particular attention given to the selectivity to C 2+ products. All catalysts were tested for CO 2 reduction in 0.1 M KHCO 3 and 0.1 M CsHCO 3 at applied voltages in the range from –0.7 to –1.0 V vs RHE. The best performing oxide-derived catalysts show up to ~70% selectivity to C 2+ products and only ~3% selectivity to C 1 products at –1.0 V vs RHE when CsHCO 3 is used as the electrolyte. In contrast, the selectivity to C 2+ products decreases to ~56% for the same catalysts tested in KHCO 3 . By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivity to C 2+ products is attained at an overpotential of –1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO 2 . On the basis of recent theoretical studies, a high pH suppresses the formation of C 1 relative to C 2+ products. At the same time, however, a high local CO 2 concentration is necessary for the formation of C 2+ products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Prediction of Adsorption Energies for Chemical Species on Metal Catalyst Surfaces Using Machine Learning

Computational catalyst screening has the potential to significantly accelerate heterogeneous catalyst discovery. Typically, this involves developing microkinetic reactor models that are based on parameters obtained from density functional theory and transition-state theory. To reduce the large computational cost involved in computing various adsorption and transition-state energies of all possible surface states on a large number of catalyst models, linear scaling relations for surface intermediates and transition states have been developed that only depend on a few, typically one or two descriptors, such as the carbon atom adsorption energy. As a result, only the descriptor values have to be computed for various active site models to generate volcano curves in activity or selectivity. Unfortunately, for more complex chemistries the predictability of linear scaling relations is unknown. Also, the selection of descriptors is essentially a trial and error process. Here, using a database of adsorption energies of the surface species involved in the decarboxylation and decarbonylation of propionic acid over eight monometalic transition-metal catalyst surfaces (Ni, Pt, Pd, Ru, Rh, Re, Cu, Ag), we tested if nonlinear machine learning (ML) models can outperform the linear scaling relations in prediction accuracy when predicting the adsorption energy for various species on a metal surface based on data from the rest of the metal surfaces. We found linear scaling relations to hold well for predictions across metals with a mean-absolute error of 0.12 eV, and ML methods being unable to outperform linear scaling relations when the training dataset contains a complete set of energies for all of the species on various metal surfaces. Only when the training dataset is incomplete, namely, contains a random subset of species’ energies for each metal, a currently unlikely scenario for catalyst screening, do kernel-based ML models significantly outperform linear scaling relations. We also found that simple coordinate-free species descriptors, such as bond counts, achieve as good results as sophisticated coordinate-based descriptors. Finally, we propose an approach for automatic discovery of appropriate metal descriptors using principal component analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Oxygen Evolution Reaction Activity in IrO x /SrIrO 3 Catalysts: Correlations between Structural Parameters and the Catalytic Activity

Understanding how structural properties affect the oxygen evolution reaction (OER) of a catalyst can reveal important information not only on the catalytic mechanism but also on the general design strategy of OER catalysts. We report a variation of ~0.15 V in the overpotential of the recently discovered IrO x /SrIrO 3 OER catalysts, which directly correlates with the structural parameters of the as-synthesized SrIrO 3 epitaxial films. This variation is caused by both extrinsic area enhancement and intrinsic electronic structure modification driven by defect formation. These correlations not only indicate that microscopic film defects play an important role in the activity of the IrO x /SrIrO 3 catalyst but also provide readily accessible parameters predictive of the activity post-transformation to IrO x /SrIrO 3 . Here, by establishing strong associations between the catalytic activity and key structural and electronic parameters, rather than synthetic variables, provides important guidance to control and study these complex catalysts independent of the synthetic technique.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Mechanistic Insights into C–H Borylation of Arenes with Organoiridium Catalysts Embedded in a Microporous Metal–Organic Framework

Organometallic iridium catalysts can be used in conjunction with bispinacolatodiboron (B 2 Pin 2 ) to effect the borylation of a variety of substrates such as arenes, alkanes, heteroarenes, and oxygenates. Recently, efforts have also focused on integrating these catalysts into porous supports, such as metal–organic frameworks (MOFs). While the mechanism of homogeneous borylation systems has been thoroughly investigated experimentally and computationally, analogous studies in MOF-supported iridium catalysts have not been conducted. In this paper, we report the mechanistic investigation of a phenanthroline-iridium catalyst immobilized in the organic linker of Universitetet i Oslo (UiO)-67 (Zr 6 O 4 (OH) 4 (BPDC) 4 (PhenDC) 2 , BPDC = biphenyl-4,4'-dicarboxylate, PhenDC = 1,10-phenanthroline-4,4'-dicarboxylate). By using benzene as a model substrate, variable time normalization analysis (VTNA) of the kinetic data suggested a rate law consistent with zero-order in B 2 Pin 2 , and first-order in arene. A primary kinetic isotope effect (KIE) in the time course of benzene-d 6 borylation also provided complementary information about the role of the arene in the rate-determining step of the reaction. Characterization by techniques such as X-ray absorption spectroscopy (XAS) confirmed the presence of Ir(III), while pair distribution function (PDF) analysis suggested structures containing an Ir–Cl bond, further substantiated by X-ray photoelectron spectroscopy (XPS). Analysis of postcatalysis materials by inductively coupled plasma–optical emission spectroscopy (ICP-OES) revealed low boron accumulation, which may indicate an absence of boron in the resting state of the catalyst. Finally, in comparing borylation of benzene and toluene, a slight selectivity for benzene is observed, which is similar to the analogous homogeneous reaction, indicating the influence of substrate sterics on reactivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Graphite Intercalation Compounds Derived by Green Chemistry as Oxygen Reduction Reaction Catalysts

Precious group metal (PGM) catalysts such as Pt supported on carbon supports are expensive catalysts utilized for the oxygen reduction reaction (ORR) due to their unmatched catalytic activity and durability. As an alternative, PGM-free ORR electrocatalysts that offer respectable catalytic activity are being pursued. Most of the notable PGM-free catalysts are obtained either from a bottom-up approach synthesis utilizing nitrogen-rich polymers as building blocks, or from a top down approach, where nitrogen and metal moieties are incorporated to carbonaceous matrixes. The systematic understanding of the origin of catalytic activity for either case is speculative and currently employed synthesis techniques typically generate large amounts of hazardous waste such as acids, oxidizing agents, and solvents. Herein, for the first time, we investigate the catalytic activity of graphite-based materials obtained via intercalation strategies that minimally perturb the graphitic backbone. Here, our outlined approaches demonstrate initial efforts to not only elucidate the role of each element but also significantly reduce the use of hazardous chemicals, which remains a pressing challenge. Graphite intercalation compounds (GIC) were obtained using fewer steps and solvent-free processes. X-ray diffraction and Raman results confirm the successful intercalation of FeCl 3 between graphite layers. Electrochemical data shows that the ORR performance of FeCl 3 -intercalated GIC displays slight improvement where the onset potential reaches 0.77 V vs RHE in alkaline environments. However, expansion of the graphite and solvent-free incorporation of iron and nitrogen moieties resulted in a significant increase in ORR activity with onset potential to 0.89 V vs RHE, a maximum half-wave of 0.72 V vs RHE, and a limiting current of about 2.5 mA cm –2 . We anticipate that the use of near solvent-free processes that result in a high yield of catalysts along with the fundamental insight into the origin of electrochemical activity will tremendously impact the methodologies for developing next-generation ORR catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Morphology Control of Carbon-Free Spinel NiCo 2 O 4 Catalysts for Enhanced Bifunctional Oxygen Reduction and Evolution in Alkaline Media

Spinel NiCo 2 O 4 is considered a promising precious metal-free catalyst that is also carbon-free for oxygen electrocatalysis. Current efforts mainly focus on optimal chemical doping and substituent to tune its electronic structures for enhanced activity. Here, we study its morphology control and elucidate the morphology-dependent catalyst performance for bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Three types of NiCo 2 O 4 catalysts with significantly distinct morphologies were prepared using temple-free, Pluronic-123 (P-123) soft, and SiO 2 hard templates, respectively, via hydrothermal methods following by a calcination. While the hard-template yields sphere-like dense structures, soft-template assists the formation of a unique nano-needle cluster assembly containing abundant meso- and macro pores. Furthermore, the effect of morphology of NiCo 2 O 4 on their corresponding bifunctional catalytic performance was systematically investigated. The flower-like nano-needle assembly NiCo 2 O 4 catalyst via the soft template method exhibited the highest catalytic activity and stability for both ORR and OER. In particular, it exhibited an onset and half-wave potentials of 0.94 and 0.82 V vs. RHE, respectively, for the ORR in alkaline media. Although it is still inferior to Pt, the NiCo 2 O 4 represents one of the best ORR catalyst compared to other reported carbon-free oxides. Meanwhile, remarkable OER activity and stability were achieved with an onset potential of 1.48 V and a current density of 15 mA/cm 2 at 1.6 V, showing no activity loss after 20,000 potential cycles (0 to 1.9 V). The demonstrated stability is even superior to Ir for the OER. The morphology-controlled approach provides an effective solution to create a robust 3D architecture with increased surface areas and enhanced mass transfer. More importantly, the soft template can yield high degree of spinel crystallinity with ideal stoichiometric ratios between Ni and Co, thus promoting structural integrity with enhanced electrical conductivity and catalytic properties.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2018

Evolution of Active Sites in Pt-Based Nanoalloy Catalysts for the Oxidation of Carbonaceous Species by Combined in Situ Infrared Spectroscopy and Total X-ray Scattering

Here, we present results from combined in situ infrared spectroscopy and total X-ray scattering studies on the evolution of catalytically active sites in exemplary binary and ternary Pt-based nanoalloys during a sequence of CO oxidation–reactivation–CO oxidation reactions. We find that when within a particular compositional range, the fresh nanoalloys may exhibit high catalytic activity for low-temperature CO oxidation. Using surface-specific atomic pair distribution functions (PDFs) extracted from the in situ total X-ray scattering data, we find that, regardless of their chemical composition and initial catalytic activity, the fresh nanoalloys suffer a significant surface structural disorder during CO oxidation. Upon reactivation in oxygen atmosphere, the surface of used nanoalloy catalysts both partially oxidizes and orders. Remarkably, it largely retains its structural state when the nanoalloys are reused as CO oxidation catalysts. The seemingly inverse structural changes of studied nanoalloy catalysts occurring under CO oxidation and reactivation conditions affect the active sites on their surface significantly. In particular, through different mechanisms, both appear to reduce the CO binding strength to the nanoalloy’s surface and thus increase the catalytic stability of the nanoalloys. The findings provide clues for further optimization of nanoalloy catalysts for the oxidation of carbonaceous species through optimizing their composition, activation, and reactivation. Besides, the findings demonstrate the usefulness of combined in situ infrared spectroscopy and total X-ray scattering coupled to surface-specific atomic PDF analysis to the ongoing effort to produce advanced catalysts for environmentally and technologically important applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Controlling Bond Scission Pathways of Isopropanol on Fe- and Pt-Modified Mo 2 N Model Surfaces and Powder Catalysts

Biomass valorization can be used to produce value-added chemicals and fuels from renewable biomass resources by upgrading them via selective bond scission while retaining certain functional groups. Specifically, upgrading biomass through the dehydrogenation of alcohols to carbonyl compounds has gained interest as a method of utilizing biomass-derived alcohols while additionally producing H 2 . In this work, isopropanol was used as a probe molecule to control bond scission selectivity over Fe- and Pt-modified molybdenum nitride (Mo 2 N) model surfaces and powder catalysts. Trends in the selectivity toward dehydration and dehydrogenation were dependent on both the type and coverage of the metal overlayer on model surfaces. These results were then extended to the corresponding powder catalysts to demonstrate how model surface studies can inform the design of supported catalysts. Density functional theory calculations provided insights into controlling the dehydration and dehydrogenation pathways. In conclusion, this work shows that a fundamental understanding of the reactivity and intermediates on Mo 2 N-based model surfaces can be applied to understand the catalytic performance of metal-modified Mo 2 N powder catalysts, and also demonstrates that Mo 2 N-based catalysts are potentially promising materials for upgrading biomass-derived oxygenates.

09 BIOMASS FUELS↗
DOE OSTI2024

Insights into the Surface Electronic Structure and Catalytic Activity of InO x /Au(111) Inverse Catalysts for CO 2 Hydrogenation to Methanol

In this article, the direct conversion of carbon dioxide (CO 2 ) into methanol (CH 3 OH) via low-temperature hydrogenation is crucial for recycling anthropogenic CO 2 emissions and producing fuels or high value chemicals. Nevertheless, it continues to be a great challenge due to the trade-off between selectivity and catalytic activity. For CO 2 hydrogenation, In 2 O 3 catalysts are known for their high CH 3 OH selectivity. Subsequent studies explored depositing metals on In 2 O 3 to enhance CO 2 conversion. Despite extensive research on metal (M) supported In 2 O 3 catalysts, the role of In-M alloys and M/In 2 O 3 interfaces in CO 2 activation and CH 3 OH selectivity remains unclear. In this work, we have examined the behavior of In/Au(111) alloys and InO x /Au(111) inverse systems during CO 2 hydrogenation using synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and catalytic tests in a batch reactor. Indium forms alloys with Au(111) after deposition. The In-Au(111) alloys display high reactivity towards CO 2 and can dissociate the molecule at room temperature to generate InO x nanostructures. At very low coverages of In (≤ 0.05 ML), the InO x nanostructures are not stable under CO 2 hydrogenation conditions and the active In-Au(111) alloys produces mainly CO and little methanol. An increase in indium coverage to 0.3 ML led to stable InOx nanostructures under CO 2 hydrogenation conditions. These InO x /Au(111) catalysts displayed a high selectivity (~ 80 %) towards CH 3 OH production and an activity for CO 2 conversion that was at least 10 times larger than that of plain In 2 O 3 or Cu(111) and Cu/ZnO(000$\overline{1)}$ benchmark catalysts. The results of AP-XPS show that InO x /Au(111) produces methanol via methoxy intermediates. Inverse oxide/metal catalysts containing InOx open up a possibility for improving CO 2 → CH 3 OH conversion in processes associated with the control of environmental pollution and the production of high value chemicals.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Mechanism of CO 2 Hydrogenation on Pd/Al 2 O 3 Catalysts: Kinetics and Transient DRIFTS-MS Studies

The hydrogenation of CO 2 was investigated over a wide range of reaction conditions, using two Pd/γ-Al 2 O 3 catalysts with different Pd loadings (5% and 0.5%) and dispersions (~11% and ~100%, respectively). Turnover rates for CO and CH 4 formation were both higher over 5% Pd/Al 2 O 3 with a larger average Pd particle size than those over 0.5% Pd/Al 2 O 3 with a smaller average particle size. The selectivity to methane (22-40%) on 5% Pd/Al 2 O 3 was higher by a factor of 2-3 than that on 0.5% Pd/Al 2 O 3 . The drastically different rate expressions and apparent energies of activation for CO and CH 4 formation lead us to conclude that reverse water gas shift and CO 2 methanation do not share the same rate-limiting step on Pd, and that the two pathways are probably catalyzed at different surface sites. Measured reaction orders in CO 2 and H 2 pressures were similar over the two catalysts, suggesting that the reaction mechanism for each pathway does not change with particle size. In accordance, the DRIFTS results reveal that the prevalent surface species and their evolution patterns are comparable on the two catalysts during transient and steady-state experiments, switching feed gases among CO 2 , H 2 and CO 2 +H 2 . The DRIFTS and MS results also demonstrate that no direct dissociation of CO 2 takes place over the two catalysts, and that CO 2 has to first react with surface hydroxyls on the oxide support. The thus-formed bicarbonates react with dissociatively adsorbed hydrogen on Pd particles to produce adsorbed formate species (bifunctional catalyst: CO 2 activation on the oxide support, and H 2 dissociation on the metal particles). Formates near the Pd particles (most likely at the metal/oxide interface) can react rapidly with adsorbed H to produce CO, which then adsorbs on the metallic Pd particles. Two types of Pd sites are identified: one has a weak interaction with CO, which easily desorbs into gas phase at reaction temperatures, while the other interacts more strongly with CO, which is mainly in multi-bound forms and remains stable in He flow at high temperatures, but is reactive towards adsorbed H atoms on Pd leading eventually to CH 4 formation. 5% Pd/Al 2 O 3 contains a larger fraction of terrace sites favorable for forming these more stable CO species than 0.5% Pd/Al 2 O 3 . Consequently, we propose that the difference in the formation rate and selectivity to CH 4 on different Pd particle sizes stems from the different concentrations of the reactive intermediate for the methanation pathway on the Pd surface. JS gratefully acknowledges the financial support of this work by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Discovering Ni/Cu Single-Atom Alloy as a Highly Active and Selective Catalyst for Direct Methane Conversion to Ethylene: A First-Principles Kinetic Study

Direct methane conversion to liquid fuels or value-added chemicals is a promising technology to utilize natural resources without resorting to further petroleum extraction. However, discovering efficient catalysts for this reaction is challenging due to either coke formation or unfavorable C-H bond activation. Herein, we design single-atom alloy (SAA) catalysts to simultaneously eliminate the above two bottlenecks based on mechanism-guided strategies: (1) the active single atom enables favorable C-H bond breaking and (2) the less reactive host metal facilitates C-C coupling and thus avoids strong binding of carbonaceous species. Employing electronic structure theory calculations, we screened the stability of multiple SAAs with 3d-5d transition metals atomically dispersed on a copper surface in terms of avoiding dopant aggregation and segregation. We then evaluated reactivities of the stable SAAs as catalysts for direct methane conversion to C2 products, including methane dehydrogenation and C-C coupling mechanisms. Combining selectivity analysis with kinetic modeling, we predicted that nickel dispersed on copper, i.e., Ni/Cu SAA, is a highly active and selective catalyst that can efficiently transform methane to ethylene. This work designs efficient SAA catalysts for direct methane activation and provides chemical insights into engineering compositions of SAAs to tune their catalytic performances.

Kothakonda, Manish↗
DOE OSTI2016

Synthesis-Structure–Function Relationships of Silica-Supported Niobium(V) Catalysts for Alkene Epoxidation with H 2 O 2

Many industrially significant selective oxidation reactions are catalyzed by supported and bulk transition metal oxides. Catalysts for the synthesis of oxygenates, and especially for epoxidation, have predominantly focused on TiO x supported on or co-condensed with SiO 2 , whereas much of the rest of Groups 4 and 5 have been less studied. We have recently demonstrated through periodic trends using a uniform molecular precursor that niobium(V)-silica catalysts reveal the highest activity and selectivity for efficient utilization of H 2 O 2 for epoxidation across all of Groups 4 and 5. In this work, we graft a wide range of Nb(V) precursors, spanning surface densities of 0.07–1.6 Nb groups nm –2 on mesoporous silica, and we characterize these materials with UV–visible spectroscopy and Nb K-edge XANES. Further, we apply in situ chemical titration with phenylphosphonic acid (PPA) in the epoxidation of cis-cyclooctene by H 2 O 2 to probe the numbers and nature of the active sites across this series and in a set of related Ti-, Zr-, Hf-, and Ta-SiO2 catalysts. By this method, the fraction of kinetically relevant NbO x species ranges from ~15% to ~65%, which correlates with spectroscopic evaluation of the NbO x sites. This titration leads to a single value for the average turnover frequency, on a per active site basis rather than a per Nb atom basis, of 1.4 ± 0.52 min –1 across the 21 materials in the series. These quantitative maps of structural properties and kinetic consequences link key catalyst descriptors of supported Nb-SiO 2 to enable rational design for next-generation oxidation catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Investigating Catalyst–Support Interactions To Improve the Hydrogen Evolution Reaction Activity of Thiomolybdate [Mo 3 S 13 ] 2– Nanoclusters

Molybdenum sulfides have been identified as promising materials for catalyzing the hydrogen evolution reaction (HER) in acid, with active edge sites that exhibit some of the highest turnover frequencies among nonpreciousmetal catalysts. The thiomolybdate [Mo 3 S 13 ] 2- nanocluster catalyst contains a structural motif that resembles the active site of MoS 2 and has been reported to be among the most active forms of molybdenum sulfide. Herein, we improve the activity of the [Mo 3 S 13 ] 2- catalysts through catalyst-support interactions. We synthesize [Mo 3 S 13 ] 2- on gold, silver, glassy carbon, and copper supports to demonstrate the ability to tune the hydrogen binding energy of [Mo 3 S 13 ] 2- using catalyst-support electronic interactions and optimize HER activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Design and Synthesis of Highly-Dispersed WO 3 Catalyst with Highly Effective NH 3 –SCR Activity for NO x Abatement

The development of high-efficiency catalysts, especially for selective catalytic reduction of NO x with NH 3 (NH 3 –SCR) catalysts, with outstanding low-temperature catalytic reactivity and impressive lifetime remains a great challenge in the field of eliminating vehicle engine exhausts. In this work, we present a novel gas-bubbling-assisted dispersed hybrid nanocrystal-assisted hydrothermal deposition (GBD-HNHD) strategy to fabricate a W@CeZrAlO x catalyst with highly dispersed WO 3 nanocrystals (10 wt %) (W@CZA-HNHD). Compared with the W/CeZrAlO x catalyst prepared with the impregnation method (W@CZA-IM), W@CZA-HNHD not only exhibits highly effective low-temperature deNO x activity (the light-off temperature being lowered 45 °C) but also shows an exceptional stability (100 h time-on-stream testing with seven measurement cycles) and long lifetime (compares well with 135,000 miles). This work not only provides a new route to prepare an advanced catalyst with high loading isolated active sites but also lays a foundation for optimizing the utilization efficiency of the catalytically active species in the practical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Atomically Dispersed Metal Catalysts for Oxygen Reduction

The unprecedented oxygen reduction reaction (ORR) activity of atomically dispersed and nitrogen-coordinated metal site (e.g., Fe, Co, or Mn) catalysts makes them promising low-cost candidates to replace platinum group metal (PGM) catalysts in proton exchange membrane fuel cells (PEMFCs). This Perspective focuses on emerging developments in mechanistic understanding, innovative synthetic concept, and performance improvement of these high-risk, high-reward PGM-free catalysts. Starting from theoretical and computational analysis of active sites and ORR pathways, here we provide a concise overview of recent progress in catalyst synthesis, characterization, and catalytic performance with an aim to elucidate structure–property correlations. We also examine remaining challenges and future directions to realize atomically dispersed metal catalysts with sufficient activity and stability for viable PEMFC applications.

08 HYDROGEN↗
DOE OSTI2018

SAPO-34/5A Zeolite Bead Catalysts for Furan Production from Xylose and Glucose

SAPO-34 zeolite crystals were grown on zeolite 5A beads, characterized, and then utilized to produce furfural from xylose and 5-hydroxymethylfurfural (HMF) from glucose. The SAPO-34/5A bead catalysts resulted in moderate furfural and HMF yields of 45% from xylose and 20% from glucose (463 K; 3 h) and were easier to recover than the SAPO-34 powder catalyst. At 463 K, the SAPO-34/5A beads were more selective than 0.02 M sulfuric acid for producing HMF and, unlike the sulfuric acid system, no levulinic acid was formed. The SAPO-34/5A bead catalysts had no significant loss in activity after three rounds of recycle when water washed or heated overnight between reactions; however, the heat-treated beads did show signs of thermal stress after the second reuse. The SAPO-34/5A bead catalysts show promise for dehydration reactions to produce furfural and HMF from xylose and glucose, respectively, and adapting the catalyst and the support bead could lead to even higher selectivities and yields.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Chemical Recycling of Polybutadiene Rubber with Tailored Depolymerization Enabled by Microencapsulated Metathesis Catalysts

The effective management of plastic waste streams to prevent plastic land and water pollution is a growing problem that is also one of the most important challenges in polymer science today. Polymer materials that are stable over their lifetime and can also be cheaply recycled or repurposed as desired could more easily be diverted from waste streams. However, this is difficult for most commodity plastics. It is especially difficult to conceive this with intractable, cross-linked polymers such as rubbers. In this work, we explore the utility of microencapsulated Grubbs’ catalysts for the in-situ depolymerization and reprocessing of polybutadiene (PB) rubber. Second-generation Hoveyda-Grubbs catalyst (HG2) contained within glassy thermoplastic microspheres can be dispersed in PB rubber below the microsphere’s glass transition temperature (T g ) without adverse depolymerization, evidenced by rubber with and without these microspheres obtaining similar shear storage moduli of ≈16 and ≈28 kPa, respectively. The thermoplastic’s T g can be used to tune the depolymerization temperature, via release of HG2 into the rubber matrix. For example, using poly(lactic acid) (PLA) vs polysulfone results in an 85 and 162 °C depolymerization temperature, respectively. Liquefaction of rubber to a mixture of small molecules and oligomers is demonstrated using a 0.01 mol % catalyst loading using PLA as the encapsulant. Furthermore, at that same catalyst loading, depolymerization occurs to a greater extent in comparison to two ex-situ approaches, including a conventional solvent-assisted method, where it occurs at roughly twice the extent at each given catalyst loading. In addition, depolymerization of the microsphere-loaded rubbers was demonstrated for samples stored under nitrogen for 23 days. Lastly, we show that the depolymerized products can be reprocessed back into solid rubber with a shear storage modulus of ≈32 kPa. Thus, we envision that this approach could be used to recycle and reuse cross-linked rubbers at the end of their product lifetime.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Selective Hydrogenation of Biomass-Derived 2(5H)-Furanone to γ-Butyrolactone over Ni-Based Bimetallic Catalysts

2(5H)-Furanone was selectively hydrogenated to γ-butyrolactone (GBL) over Ni-based bimetallic catalysts, Ni-M/SiO2 (M = Fe, Co, Cu, and Zn). Catalyst characterization showed that the metal dispersion and reducibility were changed after introducing a second metal, while the physical morphology was nearly unchanged. The most active and selective bimetallic catalyst was found to be Ni–Fe/SiO2. The reaction rate constant over the 4 wt %Ni–1 wt %Fe/SiO2 bimetallic catalyst was 0.06 min–1, doubling that over 5 wt %Ni/SiO2, and the selectivity to GBL increased slightly from 86.1 to 89.5%. The Fe/(Ni+Fe) weight ratio was changed to optimize the promoting effect of Fe. The Ni–Fe bimetallic effect was further investigated using temperature-programmed desorption experiments on single crystal model surfaces with different Fe/Ni(111) structures, revealing that the enhanced catalyst activity was mainly contributed by the formation of the Ni–Fe surface alloy.

bio-inspired↗