Periodic Reporting for period 1 - COUPC1 (Coupling strategies for scavenging reactive C1 intermediates in hydrogen generation)
Reporting period: 2020-04-01 to 2021-09-30
The largest source of greenhouse gas emissions from human activities is from burning fossil fuels for electricity, heat, and transportation. These fuels take a toll on the environment, since they cause obvious problems such as oil spills and smog filled air. The main issue being addressed with this research is the generation of alternative fuels that reduce the burning of fossil fuels. Hydrogen can be produced from diverse domestic resources with the potential for near-zero greenhouse gas emissions. Once produced, hydrogen generates electrical power in a fuel cell, emitting only water vapor and warm air. It holds promise for growth in both the stationary and transportation energy sectors.
Water-gas shift is one of the most important industrial reactions that can be used to produce hydrogen from CO/H2O mixtures and it is catalyzed by noble-metal-based catalysts, particularly Pt and Au based ones. Industrially, the most utilized catalysts are Cu/ZnO/Al2O3.
Alternatively, formic acid (HCOOH) decomposition is an important reaction due to its potential as a liquid carrier for hydrogen for use in hydrogen fuel cell technology as well as the possible role of formates as intermediates in the Water-Gas Shift reaction and Methanol synthesis. In particular, formic acid decomposition over platinum and copper-based catalysts is of interest because platinum and copper have been shown to be one of the most actives metals for HCOOH decomposition. Formic acid decomposition on platinum electrodes is also a widely-studied reaction as the elucidation of its mechanism could assist in optimizing electrocatalytic production of hydrogen and other reaction products.
The main objective of this research is to uncover previously unrecognized pathways on H2 generation mediated by reactive species, such as HCOOH, and to motivate the synthesis of the functional architectures (catalysts) for the more effective coupling of the formation and scavenging functions that are involved in the reaction. These studies will serve to recognize and control such pathways in WGS reaction where they already prevail, but are not yet evident, in order to channel reactivity and selectivity towards specific target molecules (H2 and CO2).
Water-gas shift is one of the most important industrial reactions that can be used to produce hydrogen from CO/H2O mixtures and it is catalyzed by noble-metal-based catalysts, particularly Pt and Au based ones. Industrially, the most utilized catalysts are Cu/ZnO/Al2O3.
Alternatively, formic acid (HCOOH) decomposition is an important reaction due to its potential as a liquid carrier for hydrogen for use in hydrogen fuel cell technology as well as the possible role of formates as intermediates in the Water-Gas Shift reaction and Methanol synthesis. In particular, formic acid decomposition over platinum and copper-based catalysts is of interest because platinum and copper have been shown to be one of the most actives metals for HCOOH decomposition. Formic acid decomposition on platinum electrodes is also a widely-studied reaction as the elucidation of its mechanism could assist in optimizing electrocatalytic production of hydrogen and other reaction products.
The main objective of this research is to uncover previously unrecognized pathways on H2 generation mediated by reactive species, such as HCOOH, and to motivate the synthesis of the functional architectures (catalysts) for the more effective coupling of the formation and scavenging functions that are involved in the reaction. These studies will serve to recognize and control such pathways in WGS reaction where they already prevail, but are not yet evident, in order to channel reactivity and selectivity towards specific target molecules (H2 and CO2).
The project at the University of California at Berkeley, under the supervision of Professor Enrique Iglesia, begins on June 1, 2020. During the first month of work, the researcher takes the necessary courses for safety in the laboratory. Likewise, he attends courses on the characterization of catalytic samples, so all characterization is carried out by the researcher himself, which is the reason for the acquisition of knowledge in the handling of X-ray Diffraction (XRD) or X-ray Photoelectron Spectroscopy (XPS) equipment. The researcher assembles his own reaction equipment in a fully equipped hood and in which the gas lines are available to carry out desired catalytic tests. The equipment itself has a chromatographic gas analyzer, which requires training for product analysis.
Different Cu and Pt catalysts were prepared by the researcher, supported either on Al2O3, SiO2, CeO2 or TiO2. Water-gas shift (WGS) reactions of all the prepared samples were performed on the built unit and measured rates were benchmarked against literature. This catalyst were intimately mixed with several diluents and several WGS reactions were performed, always observing a rate increase per surface metal atom, in cases where atomic contact between phases do not exist. This lack of contact in the intimate mixtures has been demonstrated by specific CO+H2 reactions where typical inhibitions of TiO2 supported materials were not detected. Therefore, the only possibility in here, as initially theorized, is the scavenging of a formed intermediate, and its derivation to CO2 and H2. The effect of temperature and different reactants cofeeding was also studied. During the first year of the project, 4 workshops regarding WGS promotion effects were given in the LSAC group.
For HCOOH decomposition project, Cu/SiO2 and Pt/SiO2 catalysts were prepared and tested. Different isotopologues (DCOOD, HCOOD and DCOOH) were also run in the unit in order to determine possible kinetic isotopic effects, determining for both catalysts the decomposition of the C-H bond as kinetically relevant step. These results were supported by the Density Functional Theory (DFT) calculations made using VASP software. Infrared experiments, combined with previously explained isotopic experiments, allowed us to determine that HCOOH decomposition followed different routes on Cu and Pt. While on the former, the H2 formation was produced with a bimolecular route in a HCOOH crowded surface, in the latter the surface is covered by strongly adsorbed CO with no detectable formate-derived species, leading to lower spaces on the metal surface for performing the catalysis. For both catalysts, accurate and experimentally reproducible rate expressions were written. During the last 6 months of the project, 2 workshops regarding HCOOH decomposition on metals were given in the LSAC group.
At the end of the project one manuscript has already been published (https://doi.org/10.1016/j.jcat.2021.08.049) regarding the study of HCOOH decomposition on Cu nanoparticles, where it was shown how crowded surfaces can facilitate catalysis by selectively stabilizing the relevant transition state more so than the precursor through interactions with more weakly bound species. This manuscript is openly accessible from virtual LSAC group library (http://iglesia.cchem.berkeley.edu/Publications.html). An additional manuscript is about to be submitted regarding HCOOH decomposition on Pt, although results still remain confidential. Preliminary results of this manuscript were disseminated during SECAT2021 congress, held in Valencia during 18-20 October 2021. Finally, at this moment, a last manuscript related to enhancement effects observed on WGS reaction is being written and it is expected to be published by mid-2022.
Different Cu and Pt catalysts were prepared by the researcher, supported either on Al2O3, SiO2, CeO2 or TiO2. Water-gas shift (WGS) reactions of all the prepared samples were performed on the built unit and measured rates were benchmarked against literature. This catalyst were intimately mixed with several diluents and several WGS reactions were performed, always observing a rate increase per surface metal atom, in cases where atomic contact between phases do not exist. This lack of contact in the intimate mixtures has been demonstrated by specific CO+H2 reactions where typical inhibitions of TiO2 supported materials were not detected. Therefore, the only possibility in here, as initially theorized, is the scavenging of a formed intermediate, and its derivation to CO2 and H2. The effect of temperature and different reactants cofeeding was also studied. During the first year of the project, 4 workshops regarding WGS promotion effects were given in the LSAC group.
For HCOOH decomposition project, Cu/SiO2 and Pt/SiO2 catalysts were prepared and tested. Different isotopologues (DCOOD, HCOOD and DCOOH) were also run in the unit in order to determine possible kinetic isotopic effects, determining for both catalysts the decomposition of the C-H bond as kinetically relevant step. These results were supported by the Density Functional Theory (DFT) calculations made using VASP software. Infrared experiments, combined with previously explained isotopic experiments, allowed us to determine that HCOOH decomposition followed different routes on Cu and Pt. While on the former, the H2 formation was produced with a bimolecular route in a HCOOH crowded surface, in the latter the surface is covered by strongly adsorbed CO with no detectable formate-derived species, leading to lower spaces on the metal surface for performing the catalysis. For both catalysts, accurate and experimentally reproducible rate expressions were written. During the last 6 months of the project, 2 workshops regarding HCOOH decomposition on metals were given in the LSAC group.
At the end of the project one manuscript has already been published (https://doi.org/10.1016/j.jcat.2021.08.049) regarding the study of HCOOH decomposition on Cu nanoparticles, where it was shown how crowded surfaces can facilitate catalysis by selectively stabilizing the relevant transition state more so than the precursor through interactions with more weakly bound species. This manuscript is openly accessible from virtual LSAC group library (http://iglesia.cchem.berkeley.edu/Publications.html). An additional manuscript is about to be submitted regarding HCOOH decomposition on Pt, although results still remain confidential. Preliminary results of this manuscript were disseminated during SECAT2021 congress, held in Valencia during 18-20 October 2021. Finally, at this moment, a last manuscript related to enhancement effects observed on WGS reaction is being written and it is expected to be published by mid-2022.
Mainly, it was found out that intimately mixing the prepared catalysts with specific diluents, such as TiO2 and CeO2, increases rates per surface metal atom up to 5 to 7 fold, indicating that atomic contact is not required for improving the catalytic activity of these samples and that certain oxides are able to derive formed intermediates to desired products by their correct positioning in the catalysts. It is expected that by the end of the project a prototype of an optimized catalyst will be prepared that would maximize H2 generation rates during water-gas shift reaction.
On the HCOOH project, it was demonstrated that its decomposition on Cu occurs on crowded surfaces that can facilitate catalysis by selectively stabilizing the relevant transition state more so than the precursor through interactions with more weakly bound species. On the other hand, same reaction on Pt supported catalysts follows a different mechanism, since reaction occurs on CO crowded surfaces, a molecule known to poison Pt electrodes during HCOOH decomposition. This will help in the development of new Pt and Cu catalyst for HCOOH decomposition, leading to more efficient H2 formation materials. Overall, the optimization of both materials will lead to the reduction of use and burning of fossil fuels and therefore, to the reduction of greenhouse gas emissions.
On the HCOOH project, it was demonstrated that its decomposition on Cu occurs on crowded surfaces that can facilitate catalysis by selectively stabilizing the relevant transition state more so than the precursor through interactions with more weakly bound species. On the other hand, same reaction on Pt supported catalysts follows a different mechanism, since reaction occurs on CO crowded surfaces, a molecule known to poison Pt electrodes during HCOOH decomposition. This will help in the development of new Pt and Cu catalyst for HCOOH decomposition, leading to more efficient H2 formation materials. Overall, the optimization of both materials will lead to the reduction of use and burning of fossil fuels and therefore, to the reduction of greenhouse gas emissions.