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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Investigation of the modes of NO adsorption in Pd/H-CHA

This study investigates NO adsorption on Pd-exchanged chabazite (Pd/H-CHA), a promising passive NO x adsorber (PNA) for capturing cold-start NO x emissions of gasoline- and diesel-powered vehicles. Here, temperature-programed desorption (TPD) and IR spectroscopy are combined with theoretical calculations to elucidate how and where NO is stored, and how water and O 2 affect this process. NO adsorption on Pd/H-CHA produces two TPD features, around 423 and 753 K, and IR bands centered at 1860 and 1810 cm –1 . Calculated NO stretching frequencies and maximum-desorption temperatures reveal that Pd 2+ and Pd + sites are responsible for these low- and high-temperature features, respectively, and that while the IR feature at 1810 cm –1 is due to NO adsorption on Pd + , the 1860 cm –1 feature contains contributions from both weakly-bound NO on Pd 2+ and more strongly bound NO on Pd + , consistent with experimentally observed effects of water and O 2 .

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

Assessment of calcium addition on the removal of U(VI) in the alkaline conditions created by NH3 gas

Remediation of uranium (U) contamination in the deep vadose zone (VZ) sediments abundant in calcite mineral is a challenging task considering the formation of highly stable and mobile uranyl complexes with carbonate and calcium in pore water composition. There is a concern that uranium contamination in the VZ can serve as a continued source for groundwater pollution, creating a risk to human health and the environment through the groundwater pathway. This requires in-situ remediation of the radionuclide-contaminated VZ to convert soluble U species to low solubility precipitates that are stable in the natural environment. Injection of reactive gasses (e.g., NH3) is a promising technology to decrease U mobility in the unsaturated zone without the addition of liquid amendments. The NH3 injection creates alkaline conditions that can alter the sediment pore water composition due to a release of elements from minerals (via desorption and dissolution) that are present in the sediment. However, it is not known how VZ pore water constituents (Si, Al3+, HCO3 -, and Ca2 +) would affect U(VI) removal/precipitation in alkaline conditions. This study quantified the role of major pore water constituents typically present in the arid and semi-arid environments of the western regions of the U.S and identified solid uranium-bearing phases that could potentially precipitate from solutions approximating pore water compositions after pH manipulations via ammonia gas injections. Triplicate samples were prepared using six Si (5, 50 100, 150, 200, and 250 mM), six HCO3 - (0, 3, 25, 50, 75, and 100 mM), and two Ca2+ (5 and 10 mM) concentrations. The concentration of aluminum and uranium was kept constant at 5mM and 0.0084 mM, respectively, in all synthetic formulations tested. Results showed that the percentage of U(VI) removal was controlled by the Si/Al molar ratios and Ca2+ concentrations. Regardless of the bicarbonate concentration tested, the percentage of U(VI) removed increased as the Si/Al ratios were increased. However, higher Ca concentrations correlated with higher U(VI) removal, ranging between 96% and 99%, at low Si/Al ratios. The SEM images of dried precipitates displayed dense amorphous regions high in silica content, where EDS elemental analysis unveiled higher U atomic percentages. The formation of uranyl silicate and carbonate minerals was also predicted by the speciation modeling. XRD analysis revealed the presence of uranyl carbonate mineral phases (andersonite, grimselite); however, uranyl silicates predicted (Naboltwoodite) were not identified experimentally, possibly due to the amorphous nature of the silica solid phases observed in our experiments.

Katsenovich, Yelena↗
DOE OSTI2026

Product-promoted acetylene cyclotrimerization to benzene on Ag(111)

Acetylene cyclotrimerization to benzene on Ag(111) has recently been found to be 100% selective. However, it requires monolayer coverages, limiting its practical application due to the high pressure required to attain this surface coverage of acetylene near room temperature. Here, we show that co-adsorbed benzene, the reaction product, promotes cyclotrimerization at submonolayer acetylene coverages without compromising the 100% selectivity of Ag(111) via temperature-programmed desorption experiments. Scanning tunneling microscopy and density functional theory (DFT) calculations elucidate the origin of this effect whereby attractive acetylene–benzene interactions locally compress acetylene domains. DFT calculations further illustrate how co-adsorbed benzene reduces the transition-state energy for formation of the key C 4 intermediate, making cyclotrimerization competitive with desorption. Together, these findings reveal how product-reactant interactions can enhance C–C coupling.

Acetylene cyclotrimerization↗
DOE OSTI2019

NH3-SCR on Cu, Fe and Cu+Fe exchanged Beta and SSZ-13 catalysts: hydrothermal aging and propylene poisoning effects

Cu, Fe and Cu+Fe ion exchanged Beta and SSZ-13 catalysts were prepared by solution ion exchange using commercial NH4/Beta, and NH4/SSZ-13 that was prepared in-house. To study hydrothermal aging effects, Beta supported catalysts were aged hydrothermally at 700 C and SSZ-13 supported catalysts were aged at 750 C. In order to reveal the effects of Fe addition in the co-exchanged catalysts, these catalysts were characterized by means of powder X-ray diffraction (XRD), N2 adsorption-desorption, electron paramagnetic resonance (EPR), 27Al-nuclear magnetic resonance (27Al-NMR) and propylene coking followed with temperature programmed reaction (TPR), and further tested with standard NH3-SCR with and without the presence of propylene. Collectively, the catalyst characterizations and reaction testing indicated minor beneficial effects of Fe addition in Cu,Fe/Beta, where NH3-SCR activity, N2 selectivity and hydrothermal stability were all slightly improved. In contrast, Fe addition did not show apparent beneficial effects in low-temperature SCR for the Cu,Fe/SSZ-13 case. At elevated reaction temperatures, however, the presence of Fe indeed considerably improved NO conversion and N2 selectivity for the hydrothermally aged Cu,Fe/SSZ-13 catalyst in the presence of propylene. The authors from Pacific Northwest National Laboratory (PNNL) gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at PNNL. PNNL is operated for the US DOE by Battelle. The authors from East China University of Science and Technology acknowledge support from National Basic Research Program of China (2013CB933200), National Natural Science Foundation of China (21577035, 21577034), Commission of Science and Technology of Shanghai Municipality (15DZ1205305) and 111 Project (B08021). Aiyong Wang also gratefully acknowledges the China Scholarship Council for a Joint-Training Scholarship Program with PNNL.

Wang, Aiyong↗
DOE OSTI2018

Theoretical Insights into Direct Methane to Methanol Conversion over Supported Dicopper Oxo Nanoclusters

In this study, the prospect of using copper oxide nanoclusters grown by atomic layer deposition on a porphyrin support for selective oxidation of methane to methanol was examined by means of density functional theory (DFT) calculations. Ab initio thermodynamic analysis indicates that an active site in the form of Cu(μ-O)Cu can be stabilized by activation in O2 at 465K. Furthermore, a moderate methane activation energy barrier (Ea=54kJ/mol) is predicted, and the hydrogen abstraction activity of the active site could be attributed to the radical character of the bridging oxygen. Methanol extraction in this system is limited by a thermodynamic barrier to desorption of ΔG=57kJ/mol at 473K; however, desorption can be facilitated by the addition of water in a “stepped conversion” process. Overall, our results indicate similar activity between porphyrin-supported copper oxide nanoclusters and existing Cu-exchanged zeolites and provide a computational proof-of-concept for utilizing functionalized organic linkers in metal-organic frameworks (MOFs) for selective oxidation of methane to methanol.

03 NATURAL GAS↗
DOE OSTI2021

Optimizing the lean hydrocarbon NO x trap: Sequential and dual-layer configurations

Vehicular emission control catalysts are ineffective in eliminating CO, hydrocarbons, and NO x during engine cold-start when exhaust temperatures are below 200 °C. In this study the performance of coupled low temperature NO x , n-C 12 H 26 (C 12 ), and C 3 H 6 trapping, release and conversion for a series of model Lean Hydrocarbon NO x Trap (LHCNT) catalysts are examined. Pd and Pt supported on small-pore (SSZ-13) and large-pore (BEA) zeolites are selected based on the performance during transient NO and C 12 uptake, release and conversion experiments. These catalysts are combined into sequential (Pt + Pd/BEA → Pd/SSZ-13; Pd/SSZ-13 → Pt + Pd/BEA) and dual-layer (Pt + Pd/BEA top, Pd/SSZ-13 bottom) configurations in an attempt to improve the trapping and conversion performance. While all three configurations trap between 75 and 100 μmolNO x /g-cat, the Pd/SSZ-13 → Pt + Pd/BEA sequential configuration is most effective in simultaneously trapping C 12 and NO in the presence of H 2 O, resulting in excellent NO and C 12 storage below 100 °C with release and/or conversion at or above 200 °C. For each configuration, C 12 oxidation lights-off below 300 °C and NO oxidation achieves ~35 % conversion in the absence of C 12 . Neither the presence of C 12 nor the order of the sequential configuration has a significant impact on NO uptake. C 12 significantly delays NO and NO 2 desorption to temperatures exceeding 300 °C. The more compact dual-layer catalyst is most effective in forming NO 2 as the release temperature lines up with the maximum NO conversion temperature but traps less C 12 than the sequential configurations. The addition of C 3 H 6 in the feed on the dual-layer catalyst leads to further delay in the NO x desorption as well as increased NO and C 12 conversion at high temperatures. Here, the overall findings provide guidance in the optimizing LHCNT configuration for realistic feeds.

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

In-situ hydrogenation of bio-oil/bio-oil phenolic compounds with secondary alcohols over a synthesized mesoporous Ni/CeO 2 catalyst

Mesoporous ceria, which was synthesized under supercritical conditions, was found to be an effective support material of Ni catalyst for the in-situ hydrogenation of m-cresol (a representative compound of bio-oil) using secondary alcohols of 2-propanol (2-PrOH) and 2-butanol (2-BuOH) as a hydrogen source (H-donor) to produce 3-methylcyclohexanol, 3-methylcyclohexene, and methylcyclohexane under a H2 gas-free atmosphere. The activities of different metal catalysts (Ni, Cu, and Co) for the in-situ hydrogenation of m-cresol were examined using 2-PrOH as a H-donor. Total and effective conversion of m-cresol achieved only over Ni/CeO 2 because of its fair catalytic properties, as determined by N2 adsorption-desorption, hydrogen temperature-programmed reduction, ammonia temperature-programmed desorption, X-ray diffraction, and transmission electron microscopy. The dependence of Ni/CeO2 performance on the reaction time (4-6 h) and Ni loading (3-9 wt%) was examined from the in-situ hydrogenation of m-cresol with 2-PrOH. The deactivation test of Ni/CeO 2 was performed by reusing the spent catalyst, which was then regenerated through successive oxidation and reduction, several times in the m-cresol transformation employing 2-PrOH as a H-donor. In addition to m-cresol, other phenolic model compounds of bio-oil, such as anisole, phenol, and guaiacol, were also treated by in-situ hydrogenation with 2-PrOH over Ni/CeO 2 . Although this catalyst was effective for phenol and guaiacol transformation, it was relatively ineffective for anisole conversion. The in-situ hydrogenation of crude bio-oil with 2-PrOH and 2-BuOH was accomplished over the Ni/CeO 2 catalyst, resulting in a refined bio-oil with a 37.5-38.9% lower oxygen content and a high heating value (HHV) of up to 25 MJ/kg.

09 BIOMASS FUELS↗
DOE OSTI2021

Nanoparticle dynamics in the spatial afterglows of nonthermal plasma synthesis reactors

Nonthermal plasma flow tube reactors are industrially scalable systems for the production of nanocrystal (NC) based materials and coatings. One key advantage of nonthermal plasma synthesis is the ability to both synthesize NCs and deposit films in a single reactor, as at the reactor outlet, NCs can be inertially deposited onto a target substrate. The size and morphology of deposited particles can substantially influence the film structure and function. Though NCs are typically near-spherical and monodispersed as-produced in plasma synthesis reactors, NC charge and growth dynamics can be altered substantially when NCs are sampled out of the plasma and through the spatial afterglow region, affecting deposition. Experiments have demonstrated changes of NC size and charge in the spatial afterglow; however, these dynamics remain unexplored and unexplained via theory and simulation. To address this, we developed a constant number Monte Carlo (CNMC) simulation model to examine the mechanisms of NC decharging and growth in the spatial afterglow of plasma flow tube reactors. Collisions between NC and plasma species, diffusive deposition, and electron desorption from NCs are incorporated in the CNMC simulation. The simulation results are specifically compared with previous experiments on Si NCs synthesized from a low pressure Ar-SiH 4 nonthermal plasma reactor. Furthermore, the experiment-model comparison shows that CNMC models can be implemented which accurately model NC size distribution evolution in a spatial afterglow. Simultaneously, results show that improved collision models, energetic species diffusion models, and electron desorption models will be necessary to accurately depict NC dynamics in spatial afterglows.

42 ENGINEERING↗
DOE OSTI2024

Performance and economic viability assessment of a novel CO 2 adsorbent for manufacturing and integration with coal power plants

Here, this study assesses the performance and economic feasibility of a novel CO 2 adsorbent for post-combustion capture in DOE/NETL’s 650 MWnet SubC PC power plant (case B11B). Bench-scale tests showed an initial adsorption capacity of 16.3 wt%, which decreased to 12.1 wt% after 41 adsorption–desorption cycles due to induced particle aggregation by over-humidification. With a conservative adsorption capacity of 8.8 wt% and 695 adsorption–desorption cycles, an adsorbent replenishment rate of 10 tonnes/h is necessary to capture 90% of CO 2 . The breakeven sale price of the adsorbent produced at this rate is $\$$1,293/tonne, which is 40 to 80 times lower than prices for K 2 CO 3 adsorbents reported in the literature (e.g., K 2 CO 3 /TiO 2 , K 2 CO 3 /ZrO 2 ) while providing better capture performances. Sensitivity analysis reveals that increasing the plant production rate from 10 to 40 tonnes/h reduces the sale price by 8%. The study also compares the CO 2 capture cost to Cansolv, an integrated solvent-based technology. The novel adsorbent requires 2.4 GJ/tonne of CO 2 for regeneration, lower than Cansolv’s 2.7 GJ/tonne. With conservative performance estimates, the capture cost is $\$$54/tonne of CO 2 , slightly higher than Cansolv’s $\$$45/tonne. To achieve lower or comparable capture costs to Cansolv, the adsorbent should meet one of the following conditions at a commercial scale: minimum 950 cycles, 16 wt% capture capacity, 50% of the adsorbent recovery, or a reduced cost to $\$$646/tonne by upscaling the manufactury to 75 tonnes/h.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2025

Efficient Synthetic Natural Gas Production from Direct Air Capture Using Titania-Based Dual Function Materials

Converting atmospheric CO2 into methane offers a compelling pathway to store intermittent renewable electricity and enhance energy security using existing natural gas infrastructure. However, current CO2 utilization approaches remain energy- and capital-intensive, largely due to the need for separate capture, purification, and conversion steps. Integrating CO2 capture with catalytic methanation represents a transformative strategy for process intensification on both the unit operation and molecular levels. We report a series of Ru-Na/TiO2 dual function materials (DFMs) for a reactive carbon capture (RCC) process consisting of simulated direct air capture and subsequent CO2 methanation (DACM). Superior methane desorption purity was observed on TiO2-based DFMs (>94 %) relative to state-of-the-art Al2O3-supported DFMs (77 %). Modifying the process to begin CO2 adsorption immediately following the methanation stage, rather than beginning adsorption near ambient temperature, resulted in >97 % methane desorption purity, suitable for injection into the natural gas pipeline without additional CO2 separation steps.

organic↗
DOE OSTI2026

Catalytic resonance theory for the kinetics of photon-promoted catalysis

The illumination of catalytic surfaces with a continuous or pulsed stream of photons dynamically modulates surface chemistry for faster rates, non-equilibrium conversion, or product selectivity control. To establish fundamental principles of dynamic photon-modulated catalysis, the photocatalytic conversion of a generic surface reaction was simulated using the kinetic Monte Carlo method to understand the kinetic implications of an independent stream of photons that promotes surface product desorption. The time-averaged photocatalytic rate at differential conditions for varying photon flux and temperatures indicated three kinetic regimes described by product thermal desorption control, surface reaction control, and an intermediate kinetic regime with a zero slope Arrhenius plot, consistent with a degree of rate control dominated by the photon arrival frequency (i.e., per-site photon flux). Here, the maximum photocatalytic rate occurred orders of magnitude above the Sabatier limit at the resonance frequency, identified as the photon arrival frequency matching the surface reaction rate constant.

Canavan, Jesse R. [University of Minnesota, Minnea↗
DOE OSTI2025

Soil porous microstructure control over soil organic matter mobility: A multimethod workflow for understanding chemistry-dependent organic matter binding in soil

Soil organic matter (SOM) has attracted a great deal of interest; particularly for its potential to mitigate human derived CO 2 emissions. Studies have demonstrated that SOM plays a critical role in carbon storage and CO 2 sequestration. However, the sorption properties of SOM, which influence its transport in pore water and stabilization within the soil, remain poorly understood. This study develops a workflow to: (1) examine compound-specific advective and diffusive transport and desorption behaviors, (2) quantify desorption rates through stop-flow and continuous-flow column experiments, and (3) evaluate the impact of soil microporosity on SOM mobility using high-resolution imaging and extractions. Intact core column experiments were conducted on Uncultivated (Natural) and Cultivated soil samples, both were arid soils, collected in Washington State. X-ray computed tomography was employed to measure porosity and pore connectivity, while Fourier-transform ion cyclotron resonance mass spectrometry was used to analyze SOM composition. The findings revealed that cultivation increased total carbon and nitrogen levels due to irrigation and fertilization, enhancing carbon capture potential in arid soils. In contrast, the Natural soil, characterized by higher porosity and connectivity, contained more oxidized carbon. Pore network analysis indicated that soil compaction in the Cultivated soil may lead to longer diffusion pathways, significantly influencing SOM transport and stability.

Hydraulic Properties↗
DOE OSTI2019

Influence of dynamic annealing of irradiation defects on the deuterium retention behaviors in tungsten irradiated with neutron

Tungsten (W) samples were damaged by neutron and 6.4 MeV Fe-ion irradiation above 1000 K simulating the divertor operation temperature. Deuterium (D) retention properties were examined by decorating the damaged W with D and subsequent thermal desorption spectroscopy (TDS) measurements. Vacancy clusters were the major D trapping site in the W irradiated with Fe-ion at 873 K, although D retention by vacancy clusters decreased in the W irradiated with Fe-ion at 1173 K due to dynamic annealing. The D de-trapping activation energy from vacancy clusters was found to be 1.85 eV. D retention in neutron damage W was larger than that damaged by Fe-ion due to the uniform distribution of irradiation defects. The D desorption behaviors from neutron damaged W was simulated well by assuming the D de-trapping activation energy to be 1.52 eV.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Performance of amine-multilayered solid sorbents for CO2 removal: Effect of fabrication variables

The emission of fossil fuel carbon dioxide (CO{sub 2) to the atmosphere is implicated as the predominant cause of global climate change; therefore, advanced CO{sub 2} capture technologies are of the utmost importance. In this study, innovative amine-multilayered sorbents were fabricated using layer-by-layer (LbL) nanoassembly technology via alternate deposition of a CO{sub 2}-adsorbing amine polymer (e.g. polyethylenimine or PEI) and an oppositely-charged polymer (e.g. polystyrene sulfonate or PSS). We found that the developed sorbents could be used for CO{sub 2} capture and that LbL nanoassembly allows us to engineer their CO{sub 2} capture performance through the fabrication variables (e.g. deposition polymers, deposition media, and number of bilayers). PEI/PSS was found to be the best polymer combination for developing sorbents with relatively high CO{sub 2} capture capacity. The amine-multilayered solid sorbents possessed fine microstructures and may have similar polymer deposition within and on the surface of solid sorbents. These amine-multilayered sorbents had much faster CO{sub 2} desorption rates compared to sorbents prepared using the current PEI-impregnation approach. Such fast CO{sub 2} desorption could make sorbents a good option for CO{sub 2} removal from power plants and even the atmosphere.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2025

Multi-scale dynamic modeling and validation of radial flow fixed bed contactors for post-combustion CO 2 capture using bench scale and pilot plant data

Here, in this work, a multi-scale model of a radial flow fixed bed contactor packed with a carbon sorbent is developed and validated with laboratory-scale and pilot plant scale dynamic data. For the lab scale system, the model results were compared with low, medium and high gas and sweep flowrates, yielding root mean square error (RMSE) of 0.80, 0.63, 0.96 CO 2 mol%, respectively, for the outlet CO 2 concentration profile considering the entire A-D cycle. For the bed outer temperature profile, maximum RMSE was found to be 5.5 °C considering all flowrates and entire A-D cycles. An experimental campaign was developed and applied to a pilot plant at Technology Center Mongstad (TCM), Norway. Approaches were developed for pre-processing of data including consideration of the effect of gas mixing, measurement delay, and determination of cyclic steady-state conditions. Considering profiles during A-D cycles for all test runs, it was found that the maximum RMSE for pressure drop, temperature for the outer section of the bed, temperature for the middle section of the bed, and outlet CO 2 concentration profile remained less than 1.5 mbar, 3.5 °C, 2.8 °C, and 1.3 CO 2 mol%, respectively. The validated model was used to perform sensitivity studies on several key design operating variables for the adsorption-desorption cycle. It was found that the flow rate and concentration of flue gas have dominant nonlinear effects on the breakthrough time while the desorption time was strongly affected by the sweep gas flowrate for the specific sorbent being evaluated in this study.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2021

The influence of LiH and TiH 2 on hydrogen storage in MgB 2 I: Promotion of bulk hydrogenation at reduced temperature

Mg(BH 4 ) 2 is an attractive hydrogen storage material, owing to its high gravimetric capacity of 14.9 wt %. However, the dehydrogenated material MgB 2 is very difficult to rehydrogenate, requiring excessive pressures and temperatures. Here we report the influence of LiH and TiH 2 on hydrogen storage reactions involving Bulk MgB 2 using XRD, XAS, FTIR and NMR. In ball-milled mixtures of LiH/MgB 2 , the LiH loses crystallinity but remains undissociated, forming a weakly bound complex with MgB 2 . The weak interactions produce minor variations in the local electronic structure at B and Mg, but do not markedly affect the underlying MgB 2 hexagonal crystal structure. No evidence is found for a mixed-metal boride Mg 1-x Li x B 2 in the as-prepared LiH/MgB 2 materials. The presence of LiH dramatically improves the hydrogenation of MgB 2 at 700 bar, forming borohydride 100 °C below the minimum hydrogenation temperature of pure MgB 2 and without the formation of undesirable intermediates such as [B 3 H 8 ] - , [B 10 H 10 ] 2- or [B 12 H 12 ] 2- . Evidence is reported for a mixed-metal borohydride of the type Mg (3-x)/2 Li x (BH 4 ) 3 produced by the hydrogenation. Subsequent desorption is also improved compared to pure Mg(BH 4 ) 2 and LiBH 4 , showing single-step hydrogen release up to ~8 wt% by 380 °C, whereas Mg(BH 4 ) 2 and LiBH 4 still retain significant amounts of hydrogen at this temperature. The material produced by desorption contains both MgB 2 and Mg metal, revealing the original LiH/MgB 2 system is not fully reversible. In contrast to LiH, TiH 2 is essentially inert when ball-milled with MgB 2 , and high-pressure hydrogenation leaves only unreacted TiH 2 and MgB 2 . Thus, added TiH 2 provides no benefit to MgB 2 hydrogenation.

08 HYDROGEN↗
DOE OSTI2023

Lithium promotion of Pt/m-ZrO 2 catalysts for low temperature water-gas shift

Low temperature water-gas shift (LTS) is an important reaction occurring in a fuel processor for producing and purifying hydrogen. Platinum supported on m-ZrO 2 belongs to a family of catalysts consisting of metal nanoparticles and an active partially reducible oxide, with the catalysis proposed to occur at the boundary between metal particles and the support. In this investigation, increasing the loading of lithium dopant increased the LTS rate up to 0.54 wt % lithium, where conversion was 2.4 times that of the unpromoted catalyst at 260°C. Further increases in lithium loading up to 1.5 wt % decreased the rate, although it remained higher than that of the unpromoted catalyst. Infrared spectroscopy and CO 2 temperature programmed desorption experiments showed three effects with increasing lithium loading: (1) lithium promoter weakened the C–H bond of formate, the proposed rate limiting step of the interfacial surface formate mechanism; (2) high levels of lithium suppressed the platinum site capacity required for hydrogen transfer; and (3) high levels of lithium increased catalyst basicity. Aspects (2) and (3) tended to inhibit desorption of product CO 2 , an acidic molecule the removal of which is metal-catalyzed. XANES and XPS experiments revealed that electron transfer to enrich Pt nanoparticles is unlikely the root cause of C–H bond weakening in formate. However, other electronic effects (e.g., electrostatic effects or molecular rearrangement due to enhanced basicity) were not ruled out.

08 HYDROGEN↗