Improving hydrothermal stability of carbon-supported metal catalysts for biomass conversions

Human civilization and modern development relies on energy, fuels, and chemicals. Since the mid-late 1700s fossil carbons have been the major source of our energy and chemicals. This continues to pose environmental concerns such as greenhouse gas emission and concerns about its unsustainable nature. As a result, developing alternative clean and renewable energy and chemicals is one of the most urgent challenges facing humanity. Biomass have demonstrated the potential to be upgraded to fuels and chemicals with several challenges to be addressed. Hydrothermal stability of catalyst is one of the challenges as many biomass conversion reactions are happening in aqueous phase. In the first chapter, general concerns about fossil fuels were discussed, followed by an overview of biomass conversion to both fuels and chemicals. The challenges facing biomass conversion were discussed including hydrothermal stability of the catalyst. Hydrothermal stability of common catalyst supports was summarized and compared. We also demonstrated different deactivation mechanisms of catalyst during hydrothermal conditions. Several strategies to improve the hydrothermal stability of catalyst were also raised. In the second chapter, we used the different pyrolysis temperature to tune the surface chemistry of the carbon coated SBA-15 support. Hydrothermal treatments and reactions were performed on the supported Pd catalyst to investigate the hydrothermal stability of the Pd particles. Through detailed 13C NMR, carbon surface chemistry was analyzed and compared in a systematic way. A better Pd stability was found on low-temperature synthesized carbon supports with more oxygen-functional groups. Leaching and sintering was the main reason for deactivation of the catalyst. In the third chapter, a nitrogen-doped carbon coated SBA-15 supported Pd material was synthesized. The catalyst showed improved stability than the only carbon coated SBA-15 supported Pd catalyst with reduced sintering and leaching. 15N and 13C NMR revealed the nitrogen, oxygen and carbon surface chemistry of the catalyst. The mesoporous structure of SBA-15 was found collapsed during the hydrothermal treatment and reactions without diminishing the stability and activity of Pd particles. Further nitrogen-doped carbon coating on CMK-3 support showed the potential application to other materials. The improved stability of Pd nanoparticles on Pd 300NC materials was ascribed to the synergistic effect of oxygen and nitrogen heteroatoms as well as decorative carbon overlayer on Pd nanoparticles. In the fourth chapter, carbon deposition and sintering was found to be a major deactivation mechanism on the carbon supported Pt catalyst. A new PANI XC72R was found to be able to stabilize Pt particles with minimum sintering. Besides, a simple regeneration method including low temperature air oxidation and H2 reduction was effective to fully recover the catalytic activity without affecting the carbon support over long time on stream. The regeneration helped to remove the carbon deposits on the catalyst and redisperse Pt particles. The same regeneration method was found effective on Ru catalysts. Future directions will be focused on further improving the hydrothermal stability of the catalyst including fundamental understanding the deactivation mechanisms and developing novel stable catalyst materials

High activity Pd-Fe bimetallic catalysts for aqueous phase hydrogenations

Palladium-iron bimetallic catalysts were synthesized using carbon-coated silica supports that provided high hydrogenation activity relative to monometallic palladium under condensed-phase hydrothermal conditions. The catalysts were applied to the hydrogenation of carbonyl groups in acetone, 2-pentanone, and propionaldehyde. While Fe incorporation independent of Pd-to-Fe ratio gave enhanced activity, the catalysts having more Fe than Pd gave more than a three-fold increase in hydrogenation activity relative to the Pd only counterpart. The activity enhancement appeared to be related to the influence of Fe on the Pd as Fe under the condensed-phase reaction conditions was inert. The catalysts were also tested for hydrogenation of unsaturated carbon-carbon double bond and aromatic rings in which more moderate activity enhancement was observed. Through evaluating the influence of Pd-to-Fe ratio on catalyst properties and catalytic performance for the range of molecules, it is proposed that the turnover frequency enhancement can be attributed to the formation of Pdδ− via Pd-Fe interaction

N- and S-doped mesoporous carbon as metal-free cathode catalysts for direct biorenewable alcohol fuel cells

Nitrogen and sulfur were simultaneously doped into the framework of mesoporous CMK-3 as metal-free catalysts for direct biorenewable alcohol fuel cells. Glucose, NH3, and thiophene were used as carbon, nitrogen and sulfur precursors, respectively, to prepare mesoporous N-S-CMK-3 with uniform mesopores and extra macropores, resulting in good O2 diffusion both in half cell and alcohol fuel cell investigations. Among all investigated CMK-3 based catalysts, N-S-CMK-3 prepared at 800 °C exhibited the highest ORR activity with the onset potential of 0.92 V vs. RHE, Tafel slope of 68 mV dec−1, and 3.96 electron transfer number per oxygen molecule in 0.1 M KOH. The alkaline membrane-based direct alcohol fuel cell (DAFC) with N-S-CMK-3 cathode displayed 88.2 mW cm−2 peak power density without obvious O2 diffusion issue, reaching 84% initial performance of that with a Pt/C cathode. The high catalyst durability and fuel-crossover tolerance led to stable performance of the N-S-CMK-3 cathode DAFC with 90.6 mW cm−2 peak power density after 2 h operation, while the Pt/C cathode-based DAFC lost 36.9% of its peak power density. The high ORR activity of N-S-CMK-3 can be attributed to the synergistic effect between graphitic-N and S (C–S–C structure), suggesting great potential to use N-S-CMK-3 as an alternative to noble metal catalysts in the fuel cell cathode

Improving Hydrothermal Stability of Supported Metal Catalysts for Biomass Conversions: A Review

Catalyst stability is one of the greatest challenges faced for the utilization of heterogeneous catalysts in the development of biomass conversion to chemicals and fuels. As many biomass transformations are performed in water, hydrothermal stability of supported metal catalysts is especially critical. This Review aims to increase attention on the hydrothermal stability of supported metal catalysts by looking at the stability of common catalyst supports, deactivation modes, and strategies to improve their durability. While common oxides such as silica, alumina, zeolite, and zirconia are not stable to hydrolytic attack, carbon, and titania show promising resistance. In addition to catalyst support leaching, amorphization, and collapse caused by hydrothermal conditions, supported metal catalysts can deactivate by sintering, leaching, poisoning, carbon deposition, and restructuring of the active metal sites. Several strategies are discussed to improve stability of supported metal catalysts: coating on the oxide, overcoating on the supported metal catalyst, metal–support interaction, embedding metal particles, bimetallic catalysts, reactor design and process optimization, and other methods. A fundamental understanding of liquid–solid interactions and deactivation mechanisms, as well as strategies to improve the catalyst durability will help to develop robust catalytic materials for the scale-up and further application of aqueous-phase biomass conversion processes

Neutrino Physics with JUNO

The Jiangmen Underground Neutrino Observatory (JUNO), a 20 kton multi-purposeunderground liquid scintillator detector, was proposed with the determinationof the neutrino mass hierarchy as a primary physics goal. It is also capable ofobserving neutrinos from terrestrial and extra-terrestrial sources, includingsupernova burst neutrinos, diffuse supernova neutrino background, geoneutrinos,atmospheric neutrinos, solar neutrinos, as well as exotic searches such asnucleon decays, dark matter, sterile neutrinos, etc. We present the physicsmotivations and the anticipated performance of the JUNO detector for variousproposed measurements. By detecting reactor antineutrinos from two power plantsat 53-km distance, JUNO will determine the neutrino mass hierarchy at a 3-4sigma significance with six years of running. The measurement of antineutrinospectrum will also lead to the precise determination of three out of the sixoscillation parameters to an accuracy of better than 1\%. Neutrino burst from atypical core-collapse supernova at 10 kpc would lead to ~5000inverse-beta-decay events and ~2000 all-flavor neutrino-proton elasticscattering events in JUNO. Detection of DSNB would provide valuable informationon the cosmic star-formation rate and the average core-collapsed neutrinoenergy spectrum. Geo-neutrinos can be detected in JUNO with a rate of ~400events per year, significantly improving the statistics of existing geoneutrinosamples. The JUNO detector is sensitive to several exotic searches, e.g. protondecay via the $p\to K^++\bar\nu$ decay channel. The JUNO detector will providea unique facility to address many outstanding crucial questions in particle andastrophysics. It holds the great potential for further advancing our quest tounderstanding the fundamental properties of neutrinos, one of the buildingblocks of our Universe

Potential of Core-Collapse Supernova Neutrino Detection at JUNO

JUNO is an underground neutrino observatory under construction in Jiangmen, China. It uses 20kton liquid scintillator as target, which enables it to detect supernova burst neutrinos of a large statistics for the next galactic core-collapse supernova (CCSN) and also pre-supernova neutrinos from the nearby CCSN progenitors. All flavors of supernova burst neutrinos can be detected by JUNO via several interaction channels, including inverse beta decay, elastic scattering on electron and proton, interactions on C12 nuclei, etc. This retains the possibility for JUNO to reconstruct the energy spectra of supernova burst neutrinos of all flavors. The real time monitoring systems based on FPGA and DAQ are under development in JUNO, which allow prompt alert and trigger-less data acquisition of CCSN events. The alert performances of both monitoring systems have been thoroughly studied using simulations. Moreover, once a CCSN is tagged, the system can give fast characterizations, such as directionality and light curve

Detection of the Diffuse Supernova Neutrino Background with JUNO

As an underground multi-purpose neutrino detector with 20 kton liquid scintillator, Jiangmen Underground Neutrino Observatory (JUNO) is competitive with and complementary to the water-Cherenkov detectors on the search for the diffuse supernova neutrino background (DSNB). Typical supernova models predict 2-4 events per year within the optimal observation window in the JUNO detector. The dominant background is from the neutral-current (NC) interaction of atmospheric neutrinos with 12C nuclei, which surpasses the DSNB by more than one order of magnitude. We evaluated the systematic uncertainty of NC background from the spread of a variety of data-driven models and further developed a method to determine NC background within 15\% with {\it{in}} {\it{situ}} measurements after ten years of running. Besides, the NC-like backgrounds can be effectively suppressed by the intrinsic pulse-shape discrimination (PSD) capabilities of liquid scintillators. In this talk, I will present in detail the improvements on NC background uncertainty evaluation, PSD discriminator development, and finally, the potential of DSNB sensitivity in JUNO

Real-time Monitoring for the Next Core-Collapse Supernova in JUNO

Core-collapse supernova (CCSN) is one of the most energetic astrophysical events in the Universe. The early and prompt detection of neutrinos before (pre-SN) and during the SN burst is a unique opportunity to realize the multi-messenger observation of the CCSN events. In this work, we describe the monitoring concept and present the sensitivity of the system to the pre-SN and SN neutrinos at the Jiangmen Underground Neutrino Observatory (JUNO), which is a 20 kton liquid scintillator detector under construction in South China. The real-time monitoring system is designed with both the prompt monitors on the electronic board and online monitors at the data acquisition stage, in order to ensure both the alert speed and alert coverage of progenitor stars. By assuming a false alert rate of 1 per year, this monitoring system can be sensitive to the pre-SN neutrinos up to the distance of about 1.6 (0.9) kpc and SN neutrinos up to about 370 (360) kpc for a progenitor mass of 30$M_{\odot}$ for the case of normal (inverted) mass ordering. The pointing ability of the CCSN is evaluated by using the accumulated event anisotropy of the inverse beta decay interactions from pre-SN or SN neutrinos, which, along with the early alert, can play important roles for the followup multi-messenger observations of the next Galactic or nearby extragalactic CCSN.Comment: 24 pages, 9 figure

Improving hydrothermal stability of carbon-supported metal catalysts for biomass conversions

Human civilization and modern development relies on energy, fuels, and chemicals. Since the mid-late 1700s fossil carbons have been the major source of our energy and chemicals. This continues to pose environmental concerns such as greenhouse gas emission and concerns about its unsustainable nature. As a result, developing alternative clean and renewable energy and chemicals is one of the most urgent challenges facing humanity. Biomass have demonstrated the potential to be upgraded to fuels and chemicals with several challenges to be addressed. Hydrothermal stability of catalyst is one of the challenges as many biomass conversion reactions are happening in aqueous phase. In the first chapter, general concerns about fossil fuels were discussed, followed by an overview of biomass conversion to both fuels and chemicals. The challenges facing biomass conversion were discussed including hydrothermal stability of the catalyst. Hydrothermal stability of common catalyst supports was summarized and compared. We also demonstrated different deactivation mechanisms of catalyst during hydrothermal conditions. Several strategies to improve the hydrothermal stability of catalyst were also raised. In the second chapter, we used the different pyrolysis temperature to tune the surface chemistry of the carbon coated SBA-15 support. Hydrothermal treatments and reactions were performed on the supported Pd catalyst to investigate the hydrothermal stability of the Pd particles. Through detailed 13C NMR, carbon surface chemistry was analyzed and compared in a systematic way. A better Pd stability was found on low-temperature synthesized carbon supports with more oxygen-functional groups. Leaching and sintering was the main reason for deactivation of the catalyst. In the third chapter, a nitrogen-doped carbon coated SBA-15 supported Pd material was synthesized. The catalyst showed improved stability than the only carbon coated SBA-15 supported Pd catalyst with reduced sintering and leaching. 15N and 13C NMR revealed the nitrogen, oxygen and carbon surface chemistry of the catalyst. The mesoporous structure of SBA-15 was found collapsed during the hydrothermal treatment and reactions without diminishing the stability and activity of Pd particles. Further nitrogen-doped carbon coating on CMK-3 support showed the potential application to other materials. The improved stability of Pd nanoparticles on Pd 300NC materials was ascribed to the synergistic effect of oxygen and nitrogen heteroatoms as well as decorative carbon overlayer on Pd nanoparticles. In the fourth chapter, carbon deposition and sintering was found to be a major deactivation mechanism on the carbon supported Pt catalyst. A new PANI XC72R was found to be able to stabilize Pt particles with minimum sintering. Besides, a simple regeneration method including low temperature air oxidation and H2 reduction was effective to fully recover the catalytic activity without affecting the carbon support over long time on stream. The regeneration helped to remove the carbon deposits on the catalyst and redisperse Pt particles. The same regeneration method was found effective on Ru catalysts. Future directions will be focused on further improving the hydrothermal stability of the catalyst including fundamental understanding the deactivation mechanisms and developing novel stable catalyst materials.</p

Selective Ammonolysis of Bioderived Esters for Biobased Amide Synthesis

Amidation is an important reaction for bioderived platform molecules, which can be upgraded for use in applications such as polymers. However, fundamental understanding of the reaction especially in the presence of multiple groups is still lacking. In this study, the amidation of dimethyl fumarate, maleate, and succinate through ester ammonolysis was examined. The reaction networks and significant side reactions, such as conjugate addition and ring closing, were determined. A preliminary kinetic comparison among additional C4 and C6 esters showed a significant correlation between molecular structure and ammonolysis reactivity. Esters with a C═C double bond in the molecule backbone were found to have higher ammonolysis reactivity. To improve the selectivity to unsaturated amides rather than byproducts, the effects of thermal conditions and additives in dimethyl fumarate ammonolysis were examined. Lower temperature and decreasing methoxide ion concentration in the solution relative to the base case conditions increased the fumaramide selectivity from 67.1 to 90.6%.This article is published as Lin, Hsi-Hsin, Yan Cheng, Jiajie Huo, and Brent H. Shanks. "Selective Ammonolysis of Bioderived Esters for Biobased Amide Synthesis." ACS Omega 6, no. 44 (2021): 30040–30049. DOI: 10.1021/acsomega.1c04750. Copyright 2021 The Authors. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission