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Qi, Long

Publications and source records attributed to Qi, Long.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Molecular simulation using transfer-learned potentials for the disordered nanoscale structure of nitrogen-doped nanoporous carbons

Machine learning (ML)-based molecular dynamics (MD) simulations of the formation of a class of N-doped nanoporous carbons are performed to assess their disordered partially graphitized nanoscale structure. The study is motivated by the effectiveness of so-called nitrogen assembly carbons (NACs) for catalysis applications. Benchmark simulations for pure-C disordered graphitic systems reveal the importance of reliably capturing the vdW component of the potentials in order to accurately describe the tendency for layering of disordered graphene-like sheets. In our modeling, this is achieved by a transfer learning strategy incorporating features of the energetics from the optB88-vdW DFT functional into potentials initially trained with a less expensive functional, thereby providing a superior description of the pure-C systems. Generation from MD simulations of realistic partially graphitized structures is significantly more challenging for N-doped versus for pure C systems. However, such structures are achieved by a tailored MD simulation protocol mimicking the experimental synthesis process and in particular incorporating an annealing and subsequent quenching stages. Simulated PXRD patterns effectively reproduce the features of experimental observations for NACs, including the appearance of a prominent but broad (002) peak at around 25, and the development of another weaker feature associated with in-layer ordering of mixed C-N graphene-like sheets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Mechanism and Kinetics of Ethanol–Acetaldehyde Conversion to 1,3-Butadiene over Isolated Lewis Acid La Sites in Silanol Nests in Dealuminated Beta Zeolite

Biomass-derived ethanol (EtOH) and acetaldehyde (AcH) conversion to 1,3-butadiene (1,3-BD) is an alternative process for 1,3-BD production. The present investigation reports the preparation and characterization of isolated La sites introduced into the silanol nests in DeAlBEA as well as detailed studies of the mechanism and kinetics for the conversion of an EtOH-AcH mixture to 1,3-BD. La sites supported on DeAlBEA are found to be present as (≡SiO) 2 La-OH groups that are H-bonded with adjacent Si-OH groups, possessing high C-C coupling activity and stability, superior to state-of-the-art Y-DeAlBEA. La sites supported on silica (La-SiO 2 ) with a similar chemical structure but no H-bonding interaction with Si-OH groups were prepared for comparison. Lewis acid La sites promote AcH aldol condensation, and the activity of such sites is nearly identical for both La-DeAlBEA and La-SiO 2 . Further, the rate of C 4 product formation increases by a factor of 4.8 upon addition of EtOH to the feed of AcH over La-DeAlBEA, whereas that over La/SiO 2 remains unchanged. Investigation of the mechanism and kinetics of AcH aldol condensation and EtOH-AcH conversion to 1,3-BD revealed two C-C bond forming pathways-AcH aldol condensation by Lewis acid La sites and direct coupling of EtOH-AcH over H-bonded (≡SiO) 2 La-OH···HO-Si≡ sites. This study provides important information about the role of the local environment of isolated Lewis acid sites and their effects on the direct coupling of EtOH and AcH to form 1,3-BD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Enhanced Activity from Coordinatively Unsaturated and Dynamic Zeolite-Bound Organoscandium Species

Scandium borohydride grafted into the micropores of the faujasite zeolite HY30 catalyzes the C–H borylation of benzene, whereas silica-grafted species are inactive. This catalytic activity may originate from grafting at a Brønsted acid site leading to a more electron-deficient rare earth center. Herein, we apply multinuclear double-resonance nuclear magnetic resonance (NMR) experiments to probe the structure and dynamics of zeolite- and silica-bound scandium borohydride complexes. The experiments reveal that scandium centers located within the zeolite micropores, in proximity to Al-created Brønsted sites, are more dynamic than rigid scandium sites grafted on silanols. Through a combination of NMR and molecular dynamics simulations, we show that the coordination of the scandium in the zeolite is labile, with the metal exchanging between two binding sites. As a result, the weak electron donation from the support that enables the movement of the Sc center leads to the formation of an undercoordinated metal center that cannot exist on silica, ultimately leading to the new catalytic activity of the species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

A US perspective on closing the carbon cycle to defossilize difficult-to-electrify segments of our economy

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. Here, we discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets.

09 BIOMASS FUELS↗
DOE OSTI2024

Supported Platinum Nanoparticles Catalyzed Carbon–Carbon Bond Cleavage of Polyolefins: Role of the Oxide Support Acidity

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/M x O y catalysts (M x O y = SrTiO 3 and SiO 2 -Al 2 O 3 ; 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(H 2 ) = 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/SrTiO 3 formed saturated hydrocarbons with negligible branching, Pt/SiO 2 -Al 2 O 3 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/SiO 2 -Al 2 O 3 compared to Pt/SrTiO 3 . 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.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Catalytic Hydrogenolysis of Polyethylene Under Reactive Separation

Deconstruction of polyolefins by catalytic hydrogenolysis is typically accompanied by the generation of undesired light gases. At reaction temperatures, the desired liquid products also tend to be volatile. Secondary cleavage of these liquid products contributes to light gas formation. The latter process was mitigated by reactive separation, continuously separating the liquid products from the catalyst throughout the experiment. At equivalent conversion, the yield and selectivity for oligomeric liquid species are increased under reactive separation, even though the carbon–carbon bond cleavage rate is slower than that in sealed experiments. More light gas is formed in the sealed reactor. Under 1 atm H 2 partial pressure, alkenes accompany the typical alkane hydrogenolysis products. Further, the alkene yield is higher, with greater selectivity for valuable α-olefins under reactive separation. These results provide the mechanistic insight that terminal alkenes are primary products of carbon–carbon bond cleavage during hydrogenolysis under experimental conditions, and secondary deconstruction of these species produces light gases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Removing Fluoride from Double Four-Membered Rings Yielding Defect-Free Zeolites under Mild Conditions Using Ozone

We have investigated ozone treatment of as-made LTA zeolites under mild temperature conditions (175 °C) using experiments and periodic DFT as a method of energy savings and engineering defects such as silanol nests in comparison with conventional calcination at 550 °C. We have studied ozone treatment on LTA samples synthesized with 1,2-dimethyl-3-(4-methylbenzyl) imidazolium (denoted as “BULKY”) as the primary organic structure-directing agent (OSDA) and with various amounts of tetramethylammonium (TMA) as a secondary OSDA. Ozone treatment of LTA-BULKY at 175 °C was found to give defect-free, pristine LTA materials as determined by 29 Si NMR, 13 C NMR, Raman spectra, and DFT to assign the spectra. This represents a significant and unexpected finding: that fluoride ions can be completely removed from double four-membered rings (D4Rs) under such mild conditions. Furthermore, ozone treatment of LTA-BULKY-TMA samples removed BULKY but left behind TMA/F, giving a new and more diverse structural landscape of Si environments in LTA. Ab initio MetaDynamics calculations provide pathways with relatively low barriers, explaining how fluoride ions can be removed from D4Rs, leaving behind defect-free LTA materials under mild conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mechanistic Insights into Processive Polyethylene Hydrogenolysis through In Situ NMR

Chemical polymer upcycling by processive catalysts is a promising plastic waste remediation strategy, with the capability of producing selective, high-value products from waste plastics with minimal energy input. We previously designed a novel processive catalyst with a mesoporous SiO 2 shell/Pt nanoparticle/SiO 2 core architecture (mSiO 2 /Pt/SiO 2 ) that deconstructs polyolefins within narrow pores. Here, in this paper, we elucidate the mechanism of processive polyolefin hydrogenolysis using in situ magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and coarse-grained molecular dynamics simulations. We observe that most polyethylene–Pt interactions do not lead to C–C bond cleavage but rather to the release of the polymer via a dehydrogenation–rehydrogenation cycle. The porous architecture increases the likelihood that a released polymer is later cleaved and enables the catalyst to perform multiple successive cleavages to the same polymer chain. Both experiment and simulation show that the extent of processivity is strongly correlated with the length of the pores, with longer pores leading to a higher processivity.

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

Ultrasmall amorphous zirconia nanoparticles catalyse polyolefin hydrogenolysis

Carbon–carbon bond cleavage reactions, adapted to deconstruct aliphatic hydrocarbon polymers and recover the intrinsic energy and carbon value in plastic waste, have typically been catalysed by metal nanoparticles or air-sensitive organometallics. Metal oxides that serve as supports for these catalysts are typically considered to be inert. Here we show that Earth-abundant, non-reducible zirconia catalyses the hydrogenolysis of polyolefins with activity rivalling that of precious metal nanoparticles. To harness this unusual reactivity, our catalytic architecture localizes ultrasmall amorphous zirconia nanoparticles between two fused platelets of mesoporous silica. Macromolecules translocate from bulk through radial mesopores to the highly active zirconia particles, where the chains undergo selective hydrogenolytic cleavage into a narrow, C18-centred distribution. Calculations indicated that C–H bond heterolysis across a Zr–O bond of a Zr(O) 2 adatom model for unsaturated surface sites gives a zirconium hydrocarbyl, which cleaves a C–C bond via β-alkyl elimination.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Supported Lanthanum Borohydride Catalyzes CH Borylation Inside Zeolite Micropores

Abstract The zeolite‐supported lanthanide La(BH 4 ) x ‐HY 30 catalyzes C−H borylation of benzene with pinacolborane (HBpin), providing a complementary approach to precious, late transition metal‐catalyzed borylations. The reactive catalytic species are generated from La grafted at the Brønsted acid sites (BAS) in micropores of the zeolite, whereas silanoate‐ and aluminoate‐grafted sites are inactive under the reaction conditions. During typical catalytic borylations, conversion to phenyl pinacolborane (PhBpin) is zero‐order in HBpin concentration. A turnover number (TON) of 167 is accessed by capping external silanols, selectively grafting at BAS sites, and adding HBpin slowly to the reaction.

Li, Yuting↗
DOE OSTI2022

Supported Lanthanum Borohydride Catalyzes CH Borylation Inside Zeolite Micropores

Abstract The zeolite‐supported lanthanide La(BH 4 ) x ‐HY 30 catalyzes C−H borylation of benzene with pinacolborane (HBpin), providing a complementary approach to precious, late transition metal‐catalyzed borylations. The reactive catalytic species are generated from La grafted at the Brønsted acid sites (BAS) in micropores of the zeolite, whereas silanoate‐ and aluminoate‐grafted sites are inactive under the reaction conditions. During typical catalytic borylations, conversion to phenyl pinacolborane (PhBpin) is zero‐order in HBpin concentration. A turnover number (TON) of 167 is accessed by capping external silanols, selectively grafting at BAS sites, and adding HBpin slowly to the reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Titrating Controlled Defects into Si-LTA Zeolite Crystals Using Multiple Organic Structure-Directing Agents

Controlling defects in zeolites is crucial for tuning their adsorption and catalytic properties. In this work, we have performed an integrated zeolite synthesis, spectroscopy, and density functional theory study to test the limit of F– as a charge-balancing agent that mitigates defects in siliceous zeolites. We focused on the synthesis of siliceous zeolite LTA at 150 °C with 1,2-dimethyl-3-(4-methylbenzyl) imidazolium as the primary organic structure-directing agent (OSDA) and tetramethyl ammonium (TMA) as the secondary OSDA. By varying the amount of TMA in the synthesis gel, positive charges were titrated into the resulting as-made Si-LTA. Surprisingly, we found that greater TMA concentration does not induce more F– to enter into the zeolite. 29Si solid-state MAS NMR, Raman spectroscopy, and density functional theory suggest that this system has surpassed its capacity for F– to balance OSDA charge, and additional positive charge is balanced by Si–O– framework defects. The number of defects in the as-made Si-LTA can be precisely titrated by the amount of TMA in the zeolite structures. For the Si-LTA synthesized without TMA, framework defects formed in the early stage of crystal growth were found to heal during later crystallization, leading to defect-free Si-LTA. However, for the Si-LTA synthesized with TMA, the defects formed in early stages do not heal. A DFT thermodynamic analysis explains that crowding of Si-LTA pores by TMA impedes defect healing; this prediction is corroborated by synthesis experiments at an elevated temperature (170 °C). These results indicate that F– can have a limited capacity to balance OSDA charge in zeolite synthesis, opening up a third route to zeolite synthesis intermediate between the fluoride and hydroxide routes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗