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Tzia Ming Onn, Sallye R. Gathmann, Silu Guo, Surya Pratap S. Solanki, Amber Walton, Benjamin J. Page, Geoffrey Rojas, Matthew Neurock, Lars C. Grabow, K. Andre Mkhoyan, Omar A. Abdelrahman, C. Daniel Frisbie, and Paul J. Dauenhauer, Journal of the American Chemical Society (JACS), 2022, 144(48), 22113-22127. 

DOI: 10.1021/jacs.2c09481

Accelerating catalytic chemistry and tuning surface reactions require precise control of the electron density of metal atoms. In this work, nanoclusters of platinum were supported on a graphene sheet within a catalytic condenser device that facilitated electron or hole accumulation in the platinum active sites with negative or positive applied potential, respectively. The catalytic condenser was fabricated by depositing on top of a p-type Si wafer an amorphous HfO₂ dielectric (70 nm), on which was placed the active layer of 2–4 nm platinum nanoclusters on graphene. A potential of ±6 V applied to the Pt/graphene layer relative to the silicon electrode moved electrons into or out of the active sites of Pt, attaining charge densities more than 1% of an electron or hole per surface Pt atom. At a level of charge condensation of ±10% of an electron per surface atom, the binding energy of carbon monoxide to a Pt(111) surface was computed via density functional theory to change 24 kJ mol^–1 (0.25 eV), which was consistent with the range of carbon monoxide binding energies determined from temperature-programmed desorption (ΔBE_CO of 20 ± 1 kJ mol^–1 or 0.19 eV) and equilibrium surface coverage measurements (ΔBE_CO of 14 ± 1 kJ mol^–1 or 0.14 eV). Impedance spectroscopy indicated that Pt/graphene condensers with potentials oscillating at 3000 Hz exhibited negligible loss in capacitance and charge accumulation, enabling programmable surface conditions at amplitudes and frequencies necessary to achieve catalytic resonance.

Tzia Ming Onn, Sallye R. Gathmann, Yuxin Wang, Roshan Patel, Silu Guo, Han Chen, Jimmy K. Soeherman, Philip Christopher, Geoffrey Rojas, K. Andre Mkhoyan, Matthew Neurock, Omar A. Abdelrahman, C. Daniel Frisbie, Paul J. Dauenhauer, Journal of the American Chemical Society Au (JACS Au), 2022, 2(5), 1123-1133.  

DOI: 10.1021/jacsau.2c00114

Publication date:  May 7, 2022

Abstract. Precise control of electron density at catalyst active sites enables regulation of surface chemistry for the optimal rate and selectivity to products. Here, an ultrathin catalytic film of amorphous alumina (4 nm) was integrated into a catalytic condenser device that enabled tunable electron depletion from the alumina active layer and correspondingly stronger Lewis acidity. The catalytic condenser had the following structure: amorphous alumina/graphene/HfO₂ dielectric (70 nm)/p-type Si. Application of positive voltages up to +3 V between graphene and the p-type Si resulted in electrons flowing out of the alumina; positive charge accumulated in the catalyst. Temperature-programmed surface reaction of thermocatalytic isopropanol (IPA) dehydration to propene on the charged alumina surface revealed a shift in the propene formation peak temperature of up to ΔT_peak∼50 °C relative to the uncharged film, consistent with a 16 kJ mol^–1 (0.17 eV) reduction in the apparent activation energy. Electrical characterization of the thin amorphous alumina film by ultraviolet photoelectron spectroscopy and scanning tunneling microscopy indicates that the film is a defective semiconductor with an appreciable density of in-gap electronic states. Density functional theory calculations of IPA binding on the pentacoordinate aluminum active sites indicate significant binding energy changes (ΔBE) up to 60 kJ mol^–1 (0.62 eV) for 0.125 e^– depletion per active site, supporting the experimental findings. Overall, the results indicate that continuous and fast electronic control of thermocatalysis can be achieved with the catalytic condenser device.

Naturally occurring metals, such as calcium, catalytically activate the intermonomer β-glycosidic bonds in long chains of cellulose, initiating reactions with volatile oxygenates for renewable applications. In this work, the millisecond kinetics of calcium-catalyzed reactions were measured via the method of the pulse-heated analysis of solid and surface reactions (PHASR) at high temperatures (370–430 °C) to reveal accelerated glycosidic ether scission with a second-order rate dependence on the Ca²⁺ ions. First-principles density functional theory (DFT) calculations were used to identify stable binding configurations for two Ca²⁺ ions that demonstrated accelerated transglycosylation kinetics, with an apparent activation barrier of 50 kcal mol–1 for a cooperative calcium-catalyzed cycle. The agreement of the mechanism with calcium cooperativity to the experimental barrier (48.7 ± 2.8 kcal mol^–1) suggests that calcium enhances the reactivity through a primary role of stabilizing charged transition states and a secondary role of disrupting native H-bonding.

LINK:  JACS Au, 2021, 1, 3, 272–281

DOI:  10.1021/jacsau.0c00092

Yutong Pang, ChoongSze Lee, ChoongSze Lee, Bess Vlaisavljevich, Christopher P. Nicholas, and Paul J. Dauenhauer, Journal of the American Chemical Society Gold (JACS Au), 2023, 3(2), 368-377. 

DOI:  10.1021/jacsau.2c00513

Publication Date:  January 9, 2023

Dehydration of methyl lactate to acrylic acid and methyl acrylate was experimentally evaluated over a Na-FAU zeolite catalyst impregnated with multifunctional diamines. 1,2-Bis(4-pyridyl)ethane (12BPE) and 4,4′-trimethylenedipyridine (44TMDP), at a nominal loading of 40 wt % or two molecules per Na-FAU supercage, afforded a dehydration selectivity of 96 ± 3% over 2000 min time on stream. Although 12BPE and 44TMDP have van der Waals diameters approximately 90% of the Na-FAU window opening diameter, both flexible diamines interact with internal active sites of Na-FAU as characterized by infrared spectroscopy. During continuous reaction at 300 °C, the amine loadings in Na-FAU remained constant for 12BPE but decreased as much as 83% for 44TMDP. Tuning the weighted hourly space velocity (WHSV) from 0.9 to 0.2 h^–1 afforded a yield as high as 92% at a selectivity of 96% with 44TMDP impregnated Na-FAU, resulting in the highest yield reported to date.

ACS Catal. 2020, 10, 21, 12666–12695

Publication Date:September 25, 2020

https://doi.org/10.1021/acscatal.0c03336

Transformational catalytic performance in rate and selectivity is obtainable through catalysts that change on the time scale of catalytic turnover frequency. In this work, dynamic catalysts are defined in the context and history of forced and passive dynamic chemical systems, with the classification of unique catalyst behaviors based on temporally relevant linear scaling parameters. The conditions leading to the catalytic rate and selectivity enhancement are described as modifying the local electronic or steric environment of the active site to independently accelerate sequential elementary steps of an overall catalytic cycle. These concepts are related to physical systems and devices that stimulate a catalyst using light, vibrations, strain, and electronic manipulations including electrocatalysis, back-gating of catalyst surfaces, and introduction of surface electric fields via solid electrolytes and ferroelectrics. These catalytic stimuli are then compared for the capability to improve catalysis across some of the most important chemical challenges for energy, materials, and sustainability.

Nature Materials, volume 19, pages 1074–1080, (2020)

Dai, H., Shen, Y., Yang, T. et al. Finned zeolite catalysts. Nat. Mater. 19, 1074–1080 (2020).

LINK:  https://doi.org/10.1038/s41563-020-0753-1

There is growing evidence for the advantages of synthesizing nanosized zeolites with markedly reduced internal diffusion limitations for enhanced performances in catalysis and adsorption. Producing zeolite crystals with sizes less than 100 nm, however, is non-trivial, often requires the use of complex organics and typically results in a small product yield. Here we present an alternative, facile approach to enhance the mass-transport properties of zeolites by the epitaxial growth of fin-like protrusions on seed crystals. We validate this generalizable methodology on two common zeolites and confirm that fins are in crystallographic registry with the underlying seeds, and that secondary growth does not impede access to the micropores. Molecular modelling and time-resolved titration experiments of finned zeolites probe internal diffusion and reveal substantial improvements in mass transport, consistent with catalytic tests of a model reaction, which show that these structures behave as pseudo-nanocrystals with sizes commensurate to that of the fin. This approach could be extended to the rational synthesis of other zeolite and aluminosilicate materials.

"A Universal Descriptor for the Entropy of Adsorbed Molecules in Confined Spaces," Paul J. Dauenhauer, Omar Abdelrahman.  ACS Central Science.  2018, 4, 9, 1235-1243.  DOI:  10.1021/acscentsci.8b00419

Publication Date:  Sept. 7, 2018

Confinement of hydrocarbons in nanoscale pockets and pores provides tunable capability for controlling molecules in catalysts, sorbents, and membranes for reaction and separation applications. While computation of the enthalpic interactions of hydrocarbons in confined spaces has improved, understanding and predicting the entropy of confined molecules remains a challenge. Here we show, using a set of nine aluminosilicate zeolite frameworks with broad variation in pore and cavity structure, that the entropy of adsorption can be predicted as a linear combination of rotational and translational entropy. The extent of entropy lost upon adsorption is predicted using only a single material descriptor, the occupiable volume (Vocc). Predictive capability of confined molecular entropy permits an understanding of the relation with adsorption enthalpy, the ability to computationally screen microporous materials, and an understanding of the role of confinement on the kinetics of molecules in confined spaces.

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Jimmy K. Soeherman, Andrew J. Jones, and Paul J. Dauenhauer, ACS Engineering Au, 2023, 3(2), 114-127. 

DOI: 10.1021/acsengineeringau.2c00043

Atmospheric carbon poses an existential threat to civilization via global climate change. Hundreds of gigatonnes of carbon dioxide must be removed from earth’s atmosphere in the next three decades, necessitating a low-cost, energy-efficient process to extract low concentrations of carbon dioxide for conversion to a stable material permanently stored for thousands of years. In this work, the challenge of removing gigatonnes of CO₂ is described via the scale of effort and the thermodynamics of collecting and reducing this diffuse chemical, the accumulation of which imparts a substantial entropy penalty on any atmospheric carbon capture process. The methods of CO₂ reduction combined with upstream direct air capture (DAC) including absorption, membrane separation, and adsorption are compared with biomass torrefaction and permanent burial (BTB). A Monte Carlo model assesses the mass, energy, and economics of the full process of biomass torrefaction from biomass collection and transport to stable carbon burial to determine that 95% of scenarios could remove carbon for less than $200 per CO₂-tonne-equivalent. Torrefied carbon is further discussed for its long-term stability and availability at the scale required to substantially mitigate the threat of climate change.

Green Chemistry, 2020,22, 4147-4160

26 March 2020

1,3-Pentadiene (piperylene) is an important monomer in the manufacturing of adhesives, plastics, and resins. It can be derived from biomass by the tandem ring-opening and dehydration (dehydra-decyclization) of 2-methyltetrahydrofuran (2-MTHF), but competing reaction pathways and the formation of another isomer (1,4-pentadiene) have limited piperylene yields to <60%. In this report, using detailed kinetic measurements of 2-MTHF dehydra-decyclization on zeolites with disparate acidities (boro-, and alumino-silicates) and micropore environments (MFI, MWW, and BEA), weakly acidic borosilicates were shown to exhibit ca. 10–30% higher selectivity to dienes at about five-to-sixty times lower proton-normalized rates than aluminosilicates (453–573 K). Dehydra-decyclization site time yields (STYs) were invariant for aluminosilicates within the investigated frameworks, indicating the absence of pore-confinement influence. However, individual site-normalized reaction rates varied by almost an order of magnitude on borosilicates in the order MWW > MFI > BEA at a given temperature (523 K), indicating the non-identical nature of active sites in these weak solid acids. The diene distribution remained far from equilibrium and was tuned towards the desirable conjugated diene (1,3-pentadiene) by facile isomerization of 1,4-pentadiene. This tuning capability was facilitated by high bed residence times, as well as the smaller micropore sizes among the zeolite frameworks considered. The suppression of competing pathways, and promotion of 1,4-pentadiene isomerization events lead to a hitherto unreported ∼86% 1,3-pentadiene yield and an overall ∼89% combined linear C5 dienes’ yield at near quantitative (∼98%) 2-MTHF conversion on the borosilicate B-MWW, without a significant reduction in diene selectivities for at least 80 hours time-on-stream under low space velocity (0.85 g reactant per g cat. per h) and high temperature (658 K) conditions. Finally, starting with iso-conversion levels (ca. 21–26%) and using total turnover numbers (TONs) accrued over the entire catalyst lifetime as the stability criterion, borosilicates were demonstrated to be significantly more stable than aluminosilicates under reaction conditions (∼3–6× higher TONs).

LINK:  https://pubs.rsc.org/en/content/articlelanding/2020/gc/d0gc00136h#!divAb...

ACS Catal. 2020, 10, 17, 9932–9942, 

Publication Date: July 13, 2020

https://doi.org/10.1021/acscatal.0c02201

It is a truth universally acknowledged that faster catalysts enable more efficient transformation of molecules to useful products and enhance the utilization of natural resources. However, the limit of static catalyst performance defined by the Sabatier principle has motivated a dynamic approach to catalyst design, whereby catalysts oscillate between varying energetic states. In this work, the concept of dynamic catalytic resonance was experimentally demonstrated via the electrocatalytic oxidation of formic acid over Pt. Oscillation of the electrodynamic potential between 0 and 0.8 V NHE via a square waveform at varying frequency (10–3 < f < 103 Hz) increased the turnover frequency to ∼20 s–1 at 100 Hz, over one order of magnitude (20×) faster than optimal potentiostatic conditions. We attribute the accelerated dynamic catalysis to nonfaradaic formic acid dehydration to surface-bound carbon monoxide at low potentials, followed by surface oxidation and desorption to carbon dioxide at high potentials.

Christoph Krumm, S. Maduskar, A.D. Paulsen, A. Anderson, N. Barberio, J. Damen, C. Beach, Satish Kumar, Paul Dauenhauer, Energy & Environmental Science 2016, 9, 1645-1649.

DOI: 10.1039/C6EE00519E

Publication Date:  March 7, 2016

Cellulosic particles on surfaces consisting of microstructured, asymmetric ratchets (100 by 400 μm) were observed to spontaneously move orthogonal to ratchet wells above the cellulose reactive Leidenfrost temperature (>750 °C). Evaluation of the accelerating particles supported the mechanism of propelling viscous forces (50–200 nN) from rectified pyrolysis vapors, thus providing the first example of biomass conveyors with no moving parts driven by high temperature for biofuel reactors.

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ACS Catal. 2019, 9, 8, 6929–6937, DOI:  10.1021/acscatal.9b01606

Acceleration of the catalytic transformation of molecules via heterogeneous materials occurs through design of active binding sites to optimally balance the requirements of all steps in a catalytic cycle. In accordance with the Sabatier principle, the characteristics of a single binding site are balanced between at least two transient phenomena, leading to maximum possible catalytic activity at a single, static condition (i.e., a “volcano curve” peak). In this work, a dynamic heterogeneous catalyst oscillating between two electronic states was evaluated via simulation, predicting catalytic activity as much as three-to-four orders of magnitude (1000–10 000) above the Sabatier maximum. Surface substrate binding energies were varied by a given amplitude (0.1 < ΔU < 3.0 eV) over a broad range of frequencies (10–4 < f < 1011 s–1) in square, sinusoidal, sawtooth, and triangular waveforms to characterize surface dynamics impact on average catalytic turnover frequency. Catalytic systems were shown to exhibit order-of-magnitude dynamic rate enhancement at “surface resonance” defined as the band of frequencies (e.g., 103–107 s–1) where the applied surface waveform kinetics were comparable to kinetics of individual microkinetic chemical reaction steps. Key dynamic performance parameters are discussed regarding industrial catalytic chemistries and implementation in physical dynamic systems operating above kilohertz frequencies.

Christoph Krumm, J. Pfaendtner, Paul Dauenhauer, Chemistry of Materials 2016, 28(9), 3108.

DOI: 10.1021/acs.chemmater.6b00580

Publication Date (Web): March 4, 2016

The mechanism of crystalline cellulose fragmentation has been debated between classical models proposing end-chain or intrachain scission to form short-chain (molten) anhydro-oligomer mixtures and volatile organic compounds. Models developed over the last few decades suggest global kinetics consistent with either mechanism, but validation of the chain-scission mechanism via measured reaction rates of cellulose has remained elusive. To resolve these differences, we introduce a new thermal-pulsing reactor four orders of magnitude faster than conventional thermogravimetic analysis (106 vs 102 °C/min) to measure the millisecond-resolved evolution of cellulose and its volatile products at 400–550 °C. By comparison of cellulose conversion and furan product formation kinetics, both mechanisms are shown to occur with the transition from chain-end scission to intrachain scission above 467 °C concurrent with liquid formation comprised of short-chain cellulose fragments.

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P. Dornath, H.J. Cho, A.D. Paulsen, P.J. Dauenhauer, W. Fan, Green Cheemistry 2015, 15, 440-447.

DOI: 10.1039/C4GC02187H

Publication Date:  November 28, 2014

Selective hydrolysis of cellulose into glucose is a critical step for producing value-added chemicals and materials from lignocellulosic biomass. In this study, we found that co-impregnation of crystalline cellulose with sulfuric acid and glucose can greatly reduce the time needed for ball milling compared with adding acid alone. The enhanced reaction time coincides with the rapid formation of branched α(1→6) glycosidic bonds, which have been shown to increase water solubility of β(1→4) glucan oligomers. Co-impregnation of glucose was crucial for the rapid formation of the α(1→6) branches, after which a carbon-based catalyst can rapidly hydrolyze the water-soluble glucan oligomers to 91.2% glucose yield faster than conventional approaches.

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M.S. Mettler, A.D. Paulsen, D.G. Vlachos, P.J. Dauenhauer, Catalysis Science and Technology 2014, 4, 3822-3825.

DOI: 10.1039/C4CY00676C

Publication Date:  June 6, 2014

Widespread adoption of biomass pyrolysis for lignocellulosic biofuels is largely hindered by a lack of economical means to stabilize the bio-oil (or pyrolysis oil) product. In this work, impregnation of supported metal catalysts provides a new approach to selectively decarbonylate primary pyrolysis products within intermediate cellulose liquid to targeted gasoline-like molecules with enhanced energy content and stability. Selective deoxygenation of hydroxy-methylfurfural (HMF) and furfural (F) to 88% yield of stable furans occurred over carbon-supported Pd, with negligible loss in overall bio-oil yield or furanic content.

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Alex D. Paulsen, Blake, R. Hough, C. Luke Williams, Andrew R. Teixeira, Daniel T. Schwartz, J. Pfaendtner, P.J. Dauenhauer, ChemSusChem 2014, 7(3), 765-776.

DOI:  10.1002/cssc.201301056

Publication Date:  February 20, 2014

Fast pyrolysis of woody biomass is a promising process capable of producing renewable transportation fuels to replace gasoline, diesel, and chemicals currently derived from nonrenewable sources. However, biomass pyrolysis is not yet economically viable and requires significant optimization before it can contribute to the existing oil-based transportation system. One method of optimization uses detailed kinetic models for predicting the products of biomass fast pyrolysis, which serve as the basis for the design of pyrolysis reactors capable of producing the highest value products. The goal of this work is to improve upon current pyrolysis models, usually derived from experiments with low heating rates and temperatures, by developing models that account for both transport and pyrolysis decomposition kinetics at high heating rates and high temperatures (>400 °C). A new experimental technique is proposed herein: spatiotemporally resolved diffuse reflectance in situ spectroscopy of particles (STR-DRiSP), which is capable of measuring biomass composition during fast pyrolysis with high spatial (10 μm) and temporal (1 ms) resolution. Compositional data were compared with a comprehensive 2D single-particle model, which incorporated a multistep, semiglobal reaction mechanism, prescribed particle shrinkage, and thermophysical properties that varied with temperature, composition, and orientation. The STR-DRiSP technique can be used to determine the transport-limited kinetic parameters of biomass decomposition for a wide variety of biomass feedstocks.

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A.R. Teixeira, R.J. Hermann, J.S. Kruger, W.J. Suszynski, L.D. Schmidt, D.P. Schmidt, P.J. Dauenhauer, ACS Sustainable Chemistry & Engineering 2013, 1, 341-348.

DOI:  10.1021/sc300148b

Publication Date:  January 18, 2013

The development of biofuels produced from biomass-derived pyrolysis oils (bio-oil) requires a deeper understanding of the bio-oil vaporization required for catalytic hydrodeoxygenation, reforming and combustion processes. Through the use of high-speed photography, bio-oil droplets on a 500 °C alumina disk in nitrogen gas were observed to undergo violent microexplosions capable of rapidly dispersing the fuel. High speed photography of the entire droplet lifetime was used to determine explosion times, frequency and evaporation rates of the bio-oil samples that have been preprocessed by filtering or addition of methanol. Filtration of the oil prior to evaporation significantly reduced the fraction of droplets that explode from 50% to below 5%. Addition of methanol to bio-oil led to uniform vaporization while also increasing the fraction of droplets that exploded. Experiments support the necessity of dissolvable solids for the formation of a volatile core and heavy shell which ruptures and rapidly expands to produce a violent bio-oil microexplosion.

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