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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Calculations of CO Oxidation over a Au/TiO 2 Catalyst: A Study of Active Sites, Catalyst Deactivation, and Moisture Effects

The reaction mechanism of CO oxidation on Au/TiO 2 catalysts remains elusive. Here, we employ density functional theory calculations to gain an understanding of several important aspects of the system, including CO adsorption, the active oxygen species, catalyst deactivation, and the promoting effect of moisture on catalytic activity. Distinct from previous theoretical studies, which tend to address these questions individually, here we construct a model of the catalytic system which can address all of the issues mentioned. For this, we have considered the complex interactions among reactants, products, and catalysts under reaction conditions. The main findings of our present study are (1) the Au/TiO 2 interface boundary can be easily oxidized, (2) CO adsorption on oxidized Au results in the formation of O–Au–CO species, (3) surface lattice oxygen on a TiO 2 support is the active oxygen species, (4) CO 2 binds strongly on the O top /Ti 5c site, forming carbonate that blocks the active site, and finally (5) water can accelerate O 2 dissociation and carbonate decomposition. The results of our theoretical model are compared with existing experimental observations and found to be largely consistent with them.

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

Combining CO 2 reduction with propane oxidative dehydrogenation over bimetallic catalysts

In this paper, the inherent variability and insufficiencies in the co-production of propylene from steam crackers has raised concerns regarding the global propylene production gap and has directed industry to develop more on-purpose propylene technologies. The oxidative dehydrogenation of propane by CO 2 (CO 2 -ODHP) can potentially fill this gap while consuming a greenhouse gas. Non-precious FeNi and precious NiPt catalysts supported on CeO 2 have been identified as promising catalysts for CO 2 -ODHP and dry reforming, respectively, in flow reactor studies conducted at 823 K. In-situ X-ray absorption spectroscopy measurements revealed the oxidation states of metals under reaction conditions and density functional theory calculations were utilized to identify the most favorable reaction pathways over the two types of catalysts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Modulating the dynamics of Brønsted acid sites on PtWOx inverse catalyst

Here metal-metal oxide (M-MO) inverse catalysts are broadly applied. Brønsted acid sites on the oxide overlayers are often hypothesized to drive selective C-O bond activation. However, the Brønsted acid site nature and dynamics under working conditions remain poorly understood due to multiple materials functionalities. Here, we investigate the formation and the dynamics of Brønsted acid and redox sites on PtWO x /C under working conditions. DFT-based thermodynamic calculations and microkinetic modeling reveal a complex interplay between Brønsted acid and redox sites and potentially fast catalyst dynamics at comparable time scales to the chemistry. Combining in situ characterization and probe chemistry, we demonstrate that the density of Brønsted acid sites on the PtWO x /C inverse catalyst could be modulated by up to two orders of magnitude by altering the reaction parameters and by the chemistry itself. We elicit an order of magnitude increase in the acid-catalyzed dehydration average reaction rate by periodic hydrogen pulsing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Hydrophenylation of ethylene using a cationic Ru( ii ) catalyst: comparison to a neutral Ru( ii ) catalyst

Charge neutral Ru(II) complexes of the type TpRu(L)(NCMe)Ph [Tp = hydridotris(pyrazolyl)borate; L = CO, PMe 3 , P(OCH 2 ) 3 CEt] have been previously reported to catalyze the hydrophenylation of ethylene (Organometallics 2012, 31, 6851-6860). Yet, catalyst longevity for the TpRu(L)(NCMe)Ph complexes is inhibited by competitive ethylene C–H activation. For example, ethylene C–H activation limits catalysis using TpRu(P(OCH 2 ) 3 CEt)(NCMe)Ph to a maximum of 20 turnover numbers for conversion of benzene and ethylene to ethylbenzene. In contrast, reaction of the cationic Ru(II) complex [(HC(pz 5 ) 3 )Ru(P(OCH 2 ) 3 CEt)(NCMe)Ph][BAr' 4 ] [HC(pz 5 ) 3 = tris(5-methyl-pyrazolyl)methane; BAr' 4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate] (0.025 mol% relative to benzene) in benzene with C 2 H 4 (15 psi) at 90 °C gives 565 turnover numbers of ethylbenzene after 131 hours. The production of 565 turnovers of ethylbenzene corresponds to an approximate one-pass 95% yield with ethylene is the limiting reagent and is a 28-fold improvement compared to the charge neutral catalyst TpRu(P(OCH 2 ) 3 CEt)(NCMe)Ph. Under identical conditions, the activity of [(HC(pz 5 ) 3 )Ru(P(OCH 2 ) 3 CEt)(NCMe)Ph][BAr' 4 ] is only 1.3 times less than TpRu(P(OCH 2 ) 3 CEt)(NCMe)Ph, but the increased stability of the cationic Ru(II) catalyst allows reactivity at much higher temperatures (up to 175 °C) and significantly enhanced rates.

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

Rate enhancement by Cu in NixCu1-x/ZrO2 bimetallic catalysts for hydrodeoxygenation of stearic acid

Hydrodeoxygenation of stearic acid on Ni/ZrO2 to n-heptadecane occurs via the reduction of stearic acid to octadecanal, followed by decarbonylation of the aldehyde to n-heptadecane. Stearic acid binds stronger than 1-octadecanal on Ni, causing decarbonylation to start only once stearic acid is almost fully converted. The rate of reduction of stearic acid to octadecanal is enhanced by addition of Cu either in the form of Cu/ZrO2 or in the form of a ZrO2 supported NixCu1-x nano-alloy. Cu has not only a higher activity for the reduction of stearic acid, it also increases the activity of Ni for decarbonylation of 1-octadecanal by increasing the electron density of Ni in the bimetal catalyst. The combination of these two effects causes the high activity of Ni-Cu bimetallic catalysts.

Denk, Christoph↗
DOE OSTI2021

CO 2 -assisted ethane oxidative dehydrogenation over MoO x catalysts supported on reducible CeO 2 –TiO 2

Supported MoO x on mixed CeO 2 –TiO 2 was investigated for the oxidative dehydrogenation of ethane (ODHE) using CO 2 as a mild oxidant. Raman spectroscopic characterization of the synthesized catalysts under dehydrated conditions suggested that surface MoO x species prefer to anchor on the crystalline domains of TiO 2 . Upon increasing the amount of CeO 2 in the mixed oxide support, significant spectral changes were observed, especially in the ~900–950 cm –1 region where Mo–O–M bonds are expected. The catalytic behaviors of Mo as opposed to pure support materials were distinct. As the ceria content in the support increased, MoO x catalysts promoted oxidative dehydrogenation pathways via the Mars–van Krevelen mechanism, while pure supports appeared to favor ethane direct dehydrogenation. Investigation of structure–function relationships via in situ Raman spectroscopic efforts revealed that adding ceria not only changed the redox properties of the support but also improved those of the deposited amorphous MoO x species. We also show that upon incorporation of ceria into the support, CO 2 directly participates in the reoxidation of the dispersed MoO x species during catalysis. Here, this effect was distinct from the participation of CO 2 in the reverse water gas shift reaction. Operando Raman spectra revealed that the presence of CO 2 prolonged the existence of the 930 cm –1 feature which appears to correlate well with the relative contribution of the oxidative versus non-oxidative pathway in ethane dehydrogenation.

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

Well-defined Pt(0) heterogeneous hydrosilylation catalysts supported by a surface bound phosphenium

Single atom, low valent transition metals are important for heterogeneous catalysis but are challenging to generate and stabilize in a well-defined manner. Herein, we explored the functionalization of silica with well-defined N-heterocyclic phosphenium (NHP) ions to heterogenize low-valent metals. The surface electro-statically bound [NHP] + coordinate to Pt(0) precursors resulting in well-defined, chemisorbed [(NHP)Pt(0)L n ] + sites. The resulting materials catalyze the hydrosilylation of alkynes and exhibit activities and selectivities that rival the current industry standard homogeneous catalysts. The catalysts leach Pt limiting their recyclability; however, recycling studies support that the high regioselectivities arise from heterogeneous sites and Pt particles do not form on the surface. Here we suspect that this phosphenium-based immobilization strategy will result in stable, tunable, low valent heterogeneous transition metal catalysts in a wider array of catalytic reactions.

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

Platinum vs transition metal carbide surfaces as catalysts for olefin and alkyne conversion: binding and hydrogenation of ethylidyne

The development of heterogeneous catalysts with activity for the hydrogenation of unsaturated hydrocarbons is of economic importance. Ethylene (C 2 H 4 ) and acetylene (C 2 H 2 ) are probe molecules useful to understand the hydrogenation mechanisms, where the most studied surfaces are Pt(111) and Pd(111), however, they have a limited activity due to the formation and accumulation of ethylidyne (CCH 3 ) species. Therefore, alternative catalysts should be developed to limit and/or avoid the formation of ethylidyne on the surface. Transition metal carbides has been reported as alternative catalysts, with the additional advantage of lower prices. The thermodynamics of ethylidyne binding and its transformations on δ-MoC(001), TiC(001), and β-Mo 2 C(100) surfaces are studied by means of periodic DFT. The results indicate that ethylidyne could be transformed to ethyl and ethane on δ-MoC(001) and TiC(001) surfaces, which are relevant species to the Horiuti-Polanyi mechanism. Therefore, these surfaces could be an alternative to Pt(111) and Pd(111), since ethylidyne could be transformed to other species, avoiding or limiting their deactivation. Conversely, ethylidyne cannot be transformed to vinyl (CHCH 2 ) or ethylene in a Horiuti-Polanyi-like mechanism; then, it is not thermodynamically feasible to use any of the studied surfaces in the selective hydrogenation of acetylene, since ethylidyne accumulation could poison the surfaces.

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

Catalyst-Vision (PEM Catalyst Layer Image Analysis Tool) [SWR-25-100]

Catalyst-Vision (PEM Catalyst Layer Image Analysis Tool) provides an advanced Python-based tool, primarily designed for use in a Jupyter/Colab notebook, for the quantitative morphological analysis of pre-segmented shapes. While developed for analyzing PEM catalyst layers from microscopy, its methodology is suitable for characterizing any grayscale object provided on a uniform white background. The tool uses a robust computer vision pipeline based on the Euclidean Distance Transform and skeletonization to accurately measure local thickness and tortuosity, providing a comprehensive characterization of an object's geometry and internal texture. If you find this code useful, please cite our preprint as: Chan, Ai-Lin and Hayden, Steven and Harvey, Steven P. and Smeaton, Michelle and Okrucky, Caleb and Watt, John and Ulična, Soňa and Spurgeon, Steven and Jungjohann, Katherine and Alia, Shaun, Mechanism-informed breakdown: understanding degradation by controlling voltage hold patterns in PEM water electrolyzers. Preprint (2025).

Spurgeon, Steven [National Laboratory of the Rocki↗
DOE OSTI2020

Peptide Control of Electrocatalyst Surface Environment and Catalyst Structure: A Design Platform to Enable Mechanistic Understanding and Synthesis of Active and Selective N2 Reduction Catalysts

Low-temperature electrochemical ammonia synthesis with heterogeneous catalysts suffers from extremely low Faradaic efficiencies (< 1%). The hydrogen evolution reaction (HER) is predicted and experimentally demonstrated to outcompete the nitrogen reduction reaction (N2RR). Meanwhile, the nitrogenase enzymes found in nature enable selective N2RR at Fe/Mo metal centers. Montoya and co-authors suggest that a successful transition metal N2RR catalyst will deviate from or completely circumvent current linear scaling relationships. We propose an approach where short-chain peptides (3-20 amino acids) will be used to control the local surface environment of catalysts. This peptide-based design strategy will be used to overcome HER selectivity and the limitations of *NxHy adsorbate scaling.

08 HYDROGEN↗
NASA NTRS1990

CO-oxidation catalysts: Low-temperature CO oxidation over Noble-Metal Reducible Oxide (NMRO) catalysts

Oxidation of CO to CO2 is an important reaction technologically and environmentally and a complex and interesting reaction scientifically. In most cases, the reaction is carried out in order to remove CO as an environmental hazard. A major application of heterogeneous catalysts is catalytic oxidation of CO in the exhaust of combustion devices. The reaction over catalysts in exhaust gas is fast and often mass-transfer-limited since exhaust gases are hot and O2/CO ratios are high. The main challenges to catalyst designers are to control thermal sintering and chemical poisoning of the active materials. The effect of the noble metal on the oxide is discussed, followed by the effect of the oxide on the noble metal, the interaction of the noble metal and oxide to form unique catalytic sites, and the possible ways in which the CO oxidation reaction is catalyzed by the NMRO materials.

Herz, Richard K.↗
DOE OSTI2021

Acid-resistant catalyst supports and catalysts

A process for preparing a catalyst comprises coating substantial internal surfaces of porous inorganic powders with titanium oxide to form titanium oxide-coated inorganic powders. After the coating, an extrudate comprising the titanium oxide-coated inorganic powders is formed and calcined to form a catalyst support. Then, the catalyst support is impregnated with a solution containing one or more salts of metal selected from the group consisting of molybdenum, cobalt, and nickel.

Schmidt, Stephen R.↗