Change In Product Distribution Research Articles

Water-Insoluble Copper Complexes As Electrocatalysts for CO2 Reduction

The electrochemical reduction of carbon dioxide (CO2R) constitutes a promising CO2 utilization technology, allowing the production of valuable fuels and chemicals by using electrical energy from renewable sources. Nevertheless, poor selectivity and high required overpotentials hamper practical applications of the CO2R, which highlights the need for the development of more efficient electrocatalysts. Different copper-based materials have been extensively studied as electrocatalysts for CO2R. Particularly, copper complexes exhibited interesting properties under operational conditions: many of them undergo structural modifications (e.g. changes in oxidation state and/or coordination number), which potentially affect activity, selectivity and stability. Interestingly, some complexes exhibit reversible restructuring under specific conditions, which can be an interesting property to reach higher stability. In this presentation, we will show the results obtained for the electrocatalysis of water-insoluble copper complexes for the CO2R. The activity, selectivity and stability of both [Cu(bzimpy)Cl2] and [Cu(pyrben)2(NO3)]NO3 were investigated in K2SO4 0.1 mol L-1 (CO2 sat.) under different electrochemical conditions. Here, bzimpy and pyrben stand for 2,6-bis(2-benzimidazolyl)pyridine and 2-(2-pyridyl)benzimidazole, respectively. Qualitative EC-MS (Electrochemistry Coupled to Mass Spectrometry) analysis evidenced that both complexes are active for CO2 reduction and that product distribution changes according to the applied potential. Quantitative gas chromatography measurements revealed that, at -1.24 V vs. RHE, [Cu(bzimpy)Cl2] promotes the formation of H2, CO, CH4 and C2H4 with faradaic efficiencies of 26, 3.4, 9.2 and 31%, respectively. On the other hand, [Cu(pyrben)2(NO3)]NO3 shows FE values of 24, 8.8, 15 and 24% for H2, CO, CH4 and C2H4, respectively. After 1.6 h of electrolysis, the former exhibited stable current and FE of ~42% towards ethylene formation.

Carbon Supported Pd Nanostructures for Electrochemical Reduction of Carbon Dioxide – Effects of Ozonation

Out of the transition metals capable of electrochemical carbon dioxide reduction, Pd is interesting as it can convert carbon dioxide electrochemically into formate or carbon monoxide depending on the applied potential. In fact, it is capable of producing formate at the most positive known potentials that are close to zero overpotentials although at an unfortunately low activity and at the cost of deactivation by carbon monoxide poisoning. One aim is to improve the activity and stability of Pd-based electrocatalysts towards formate production in low overpotentials. As Pd is a critical raw material, we also wish to decrease the amount of Pd required while maintaining high carbon dioxide electroreduction capability. These goals can be achieved by nanostructuring and supporting the Pd catalyst. Here, we have employed a simple wet impregnation synthesis approach to prepare small nanoparticles and nanowires of Pd supported on single walled carbon nanotubes and tested the optimum loading of Pd to obtain high formate yield with improved activity and stability. Reactive sites can be created on the carbon support by subjecting it to ozonation prior to supporting the metal, which may help certain interesting nanostructures, such as nanowires, to grow. Additionally, the oxygen functional groups on the carbon surface are expected to affect the wettability of the electrode which is important for achieving an efficient carbon dioxide electroreduction and a longer-term stability of the reaction. Therefore, we also studied the effects of ozonation of the carbon supports on the electrochemical reduction of carbon dioxide into both formate and syngas (mixture of hydrogen and carbon monoxide) on Pd. Carbon atoms inevitably participate in hydrogen evolution reaction and, thus, in syngas production on Pd-supported catalysts at higher overpotentials. Our results show that ozonation greatly enhances the activity of the catalyst material and improves its stability when applying low overpotentials for formate formation in comparison to the pristine carbon support. The current density on Pd supported ozone treated carbon nanotube material remains stable over 4h of carbon dioxide electrolysis at an applied potential of -0.45 V (vs. RHE) while Pd on pristine carbon support deactivates during the initial 30 min of the experiment. Longer electrolysis times do reveal slow changes in product distribution although activity on ozone-treated single walled carbon nanotube-supported catalyst is excellent. Additionally, the different support materials cause interesting changes in product selectivity upon applying higher overpotentials for the production of syngas. Pd supported on pristine nanotubes produces syngas with carbon monoxide-to-hydrogen ratios of 0.72 and 1.38 at applied potentials of -0.85 V (vs. RHE) and -0.95 V (vs. RHE), respectively, while ozone treated material produces less than 10% of carbon monoxide. Through physico-chemical characterizations of the materials we aim at understanding the observed changes in electrochemical reduction of carbon dioxide on carbon supported Pd nanostructures.

Micro-mesoporous ferrierite obtained using the cationic polymer Luviquat and post-synthesis treatment

This study investigated for the first time the synthesis of ferrierite zeolite through the vapor-phase transport method using the cationic polymer Luviquat as a mesopores-generating agent, followed by desilication treatment. The effect of ferrierite's textural and acid properties was then evaluated in the catalytic cracking of ultra-high molecular weight polyethylene (UHMWPE). The synthesized zeolites showed a crystallinity of 91%–100% and similar Si/Al ratios. After the desilication, there was a decrease in these values along with an increase in acidity, attributable to the extraction of structural silicon. The strong interaction between the polymer and the zeolite precursor during the self-assembly process led to the formation of intracrystalline mesoporosity. However, an internal diffusion limit and/or steric hindrance hinders the complete incorporation of the polymer into the ferrierite structure, especially at high polymer concentrations. Thus, the optimal composition was 40% Luviquat, which resulted in twice the volume of mesopores compared to the sample prepared without the polymer. The desilication of the samples synthesized with the Luviquat led to a substantial increase in mesoporosity, ranging from 67% to 183%, relative to microporous ferrierite. The introduction of mesoporosity and the modification of acid properties in ferrierite contributed to a reduction in the temperature for the cracking of UHMWPE, between 66 and 93 °C compared to the pure polymer. However, in all cases, there was an increase in the average apparent activation energy in relation to desilicated microporous ferrierite zeolite, possibly due to changes in product distribution.

Comparison of Catalytic Properties of the Easily Interconvertible, Water-Soluble [RuHCl(CO)(mtppms-Na)3] and [RuH(H2O)(CO)(mtppms-Na)3][BF4

The effect of the mobile interconversion of [RuHCl(CO)(mtppms-Na)3] 1, and [RuH(H2O)(CO)(mtppms-Na)3]+ 2, was studied in hydrogenation of phenylacetylene and cinnamaldehyde in aqueous–organic biphasic systems, as a function of the chloride concentration and the pH of the aqueous phase. Catalytic activity of the two complexes was also determined in homogeneous organic solvents without any additives. In the biphasic system, the rate of selective hydrogenation of phenylacetylene to styrene was strongly increased upon addition of NaCl, while the reaction of cinnamaldehyde slowed, with no change in product distribution. Both reactions responded with a rate decrease upon increasing the pH of the aqueous phase. It was concluded that hydrogenation of phenylacetylene was catalyzed by 1 with no chloride dissociation, while in the reduction of cinnamaldehyde, the aquo-complex 2 was the active catalytic species. Catalytic cycles were suggested to rationalize these findings.

Exploring optimal Taxol® CYP725A4 activity in Saccharomyces cerevisiae

BackgroundCYP725A4 catalyses the conversion of the first Taxol® precursor, taxadiene, to taxadiene-5α-ol (T5α-ol) and a range of other mono- and di-hydroxylated side products (oxygenated taxanes). Initially known to undergo a radical rebound mechanism, the recent studies have revealed that an intermediate epoxide mediates the formation of the main characterised products of the enzyme, being T5α-ol, 5(12)-oxa-3(11)-cyclotaxane (OCT) and its isomer, 5(11)-oxa-3(11)-cyclotaxane (iso-OCT) as well as taxadienediols. Besides the high side product: main product ratio and the low main product titre, CYP725A4 is also known for its slow enzymatic activity, massively hindering further progress in heterologous production of Taxol® precursors. Therefore, this study aimed to systematically explore the key parameters for improving the regioselectivity and activity of eukaryotic CYP725A4 enzyme in a whole-cell eukaryotic biocatalyst, Saccharomyces cerevisiae.ResultsInvestigating the impact of CYP725A4 and reductase gene dosages along with construction of self-sufficient proteins with strong prokaryotic reductases showed that a potential uncoupling event accelerates the formation of oxygenated taxane products of this enzyme, particularly the side products OCT and iso-OCT. Due to the harmful effect of uncoupling products and the reactive metabolites on the enzyme, the impact of flavins and irons, existing as prosthetic groups in CYP725A4 and reductase, were examined in both their precursor and ready forms, and to investigate the changes in product distribution. We observed that the flavin adenine dinucleotide improved the diterpenoids titres and biomass accumulation. Hemin was found to decrease the titre of iso-OCT and T5α-ol, without impacting the side product OCT, suggesting the latter being the major product of CYP725A4. The interaction between this iron and the iron precursor, δ-Aminolevulinic acid, seemed to improve the production of these diterpenoids, further denoting that iso-OCT and T5α-ol were the later products. While no direct correlation between cellular-level oxidative stress and oxygenated taxanes was observed, investigating the impact of salt and antioxidant on CYP725A4 further showed the significant drop in OCT titre, highlighting the possibility of enzymatic-level uncoupling event and reactivity as the major mechanism behind the enzyme activity. To characterise the product spectrum and production capacity of CYP725A4 in the absence of cell growth, resting cell assays with optimal neutral pH revealed an array of novel diterpenoids along with higher quantities of characterised diterpenoids and independence of the oxygenated product spectra from the acidity effect. Besides reporting on the full product ranges of CYP725A4 in yeast for the first time, the highest total taxanes of around 361.4 ± 52.4 mg/L including 38.1 ± 8.4 mg/L of T5α-ol was produced herein at a small, 10-mL scale by resting cell assay, where the formation of some novel diterpenoids relied on the prior existence of other diterpenes/diterpenoids as shown by statistical analyses.ConclusionsThis study shows how rational strain engineering combined with an efficient design of experiment approach systematically uncovered the promoting effect of uncoupling for optimising the formation of the early oxygenated taxane precursors of Taxol®. The provided strategies can effectively accelerate the design of more efficient Taxol®-producing yeast strains.

Inhomogeneity Effects on Reactions in Supercritical Fluids: A Computational Study on the Pyrolysis of n-Decane.

Supercritical fluids exhibit peculiar inhomogeneity, which strongly affects reaction behaviors in them. However, explanations for inhomogeneity and its effect on reactions are both ambiguous so far. Here, we provide an atomic-level understanding of inhomogeneity effects on reactions via the computational method, with the example of n-decane pyrolysis under supercritical conditions. We describe the characteristic pyrolysis behaviors through collective variable-driven hyperdynamics (CVHD) simulations and explain the inhomogeneity of supercritical n-decane as the coexistence of gas-like and liquid-like atoms by a trained machine learning classifier. Due to their specific local environment, the appearance of liquid-like atoms under supercritical conditions significantly increases the type and frequency of bimolecular reactions and eventually causes changes in product distributions. Future research with this method is expected to extend the effect of inhomogeneity on other reactions under supercritical conditions or other condensed phases.

Conversion of methanol to propylene over SAPO-14: Reaction mechanism and deactivation

Methanol to olefins (MTO) reaction as an important non-oil route to produce light olefins has been industrialized, and received over 80% ethylene plus propylene selectivity. However, to achieve high single ethylene or propylene selectivity towards the fluctuated market demand is still full of challenge. Small-pore SAPO-14 molecular sieve is a rare MTO catalyst exhibiting extra-high propylene selectivity. It provides us a valuable clue for further understanding of the relationship between molecular sieve structure and MTO catalytic performance. In this work, a seconds-level sampling fixed-bed reactor was used to capture real-time product distributions, which help to achieve more selectivity data in response to very short catalytic life of SAPO-14. Changes in product distribution, especially during the low activity stage, reflect valuable information on the reaction pathway. Combined with in situ diffuse reflectance infrared Fourier-transform spectroscopy, in situ ultraviolet Raman measurements and 12C/13C isotopic switch experiments, a reaction pathway evolution from dual cycle to olefins-based cycle dominant was revealed. In addition, the deactivation behaviors of SAPO-14 were also investigated, which revealed that polymethylbenzenes have been the deactivated species in such a situation. This work provides helpful hints on the development of characteristic methanol to propylene (MTP) catalysts.

Operando Study of MEA-Based CO2 Electrolyser over Copper Based Gas Diffusion Electrodes

CO2 electrolysis is a promising technology for a renewable feedstock of carbon-based chemicals. Membrane Electrode Assembly (MEA)-based CO2 electrolysers have been demonstrated to run at commercially relevant current densities. However, the MEA approach can suffer from an unstable production of targeted products, mainly caused by an increase in hydrogen production often within a few hours of operation. We conducted operando measurements in a custom-made electrochemical cell (with an electrode area of 64 mm2) using a high-energy synchrotron X-ray source to study CO2 electrolysis over Cu-based gas diffusion electrodes (GDEs). A series of experiments have been performed between 100 to 250 mA cm−2, showing a change in product distribution as a function of time. Expectedly, this is caused by an increase in water content in the GDE (also called as flooding of GDE) rather than any change of the catalyst itself, e.g. slow depletion of subsurface oxygen. Interestingly, we found that while the increase in water content is causing a gradual degradation of the performance, salt precipitation also had a major influence on water management as well. By having an in-line GC attached to the cell, we could monitor both cathodic and anodic performance as a function of time and relate this to variations in water content throughout the device. Variations in cations played a substantial role in modifying the hydration properties of the device adding an additional effect cations have beyond their role in catalysis. The insights generated from this work will allow future researchers to engineer devices that can maintain proper water management and thus entail long term stability.

Bio-oil production from low-rank coal via novel catalytic microwave pyrolysis using activated carbon + Fe2(SO4)3 and HZSM-5 + Fe2(SO4)3

The need for clean-coal technology is still demanding to counter environmental issues. Global coal is dominated by low-rank coal (LRC). Microwave pyrolysis (MP) is an advanced technologies to convert LRC into clean energy such as bio-oil. However, the main pyrolysis challenges are low heating efficiency and the products dominated by heavy-tars. This study focused on MP to treat LRC using AC + Fe2(SO4)3 and HZSM-5 + Fe2(SO4)3 as catalysts and receptor. Effects on product distribution and process conditions (time, temperature, and power) were evaluated. Results showed that AC + Fe2(SO4)3 and HZSM-5 + Fe2(SO4)3 increased the rate of temperature rise and final temperature of MP, causing changes in product distribution. As compared to non-microwave or conventional catalytic pyrolysis (CP) at the same condition (620℃ and 60 min), bio-oil produced from MP + 1.0%AC + 24.6%Fe2(SO4)3 was 47.1%, 13.2% higher than the CP. Meanwhile, using MP + 1.0%HZSM-5 + 24.6%Fe2(SO4)3, 42.5% bio-oil was produced by an increase of 8.6%. Using 1.0%AC + 24.6%Fe2(SO4)3, the maximum bio-oil production was observed at 120 min, 620℃, and 450 W, generating 49.2% bio-oil. Meanwhile, using 1.0%HZSM-5 + 24.6%Fe2(SO4)3, the maximum bio-oil production was observed at 105 min, 620℃, and 525 W, generating 42.2% bio-oil. The outcomes of the studies could be a basis for future clean fuel production utilizing LRC that could reduce global carbon emission.

Co-pyrolysis of torrefied biomass and coal: Effect of pressure on synergistic reactions

The co-utilization of torrefied biomass and coal in thermochemical conversion technologies is an attractive process for the transition to green energy and chemicals. The main advantage of this process is the production of high quality oil products (closer resembling crude-oil) via synergistic interaction of primary products from the two feedstocks. These synergistic reactions often involve secondary reactions, which are promoted at high pressures. This paper reports quantitative results on the extent of synergistic reactions and the role of pressure on these reactions during co-pyrolysis of torrefied biomass and coal. Torrefied biomass was produced at 280 °C in a pilot rotary kiln and subsequently both pyrolysis and co-pyrolysis of torrefied biomass and coal was investigated in a fixed bed reactor (heating rate 7 °C/min) at temperatures of 400–600 °C and pressures of 1, 15 and 30 bar. The results show that the prior removal of hemicellulose during torrefaction maximized the potential of hydrogen transfer from cellulose/lignin-derived products to depolymerized coal fragments. Furthermore, the dehydration and condensation reactions of depolymerized fragments were suppressed during co-pyrolysis in favour of synergistic reactions between the fragments. These reactions occurred predominantly in the molten/liquid phase and their rates could be indirectly controlled by pressure (through changing the evaporation rate), resulting in substantial changes in product distribution. In the presence of coal and its released vapours, the methoxyphenols (guaiacols) and furanics yields were significantly enhanced (positive deviation >54% and >40%, respectively, compared to additive predictions), whereas the phenol yields were inhibited (negative deviation >20%); suggesting the inhibition of demethoxylation reactions in the presence of coal depolymerized fragments. To date no studies have reported the molten phase synergistic reaction pathways occurring during co-pyrolysis of torrefied biomass and coal. Based on the findings in this paper, reaction pathways were proposed for these molten phase synergistic reactions.

Ce-introduced effects on modification of acidity and Pt electronic states on Pt-Sn/γ-Al2O3 catalysts for catalytic reforming

Catalytic reforming of n-heptane over a series of Pt-based catalysts modified by Sn and Ce has been conducted in a fixed-bed reactor. Introducing Sn and Ce resulted in changes in the electronic environment of the Pt particles and acidity properties of the γ-Al2O3 support, causing changes in product distribution. Results from in-situ Diffusion Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) evidenced that the metal promoters altered the metal-support interaction, endowing the generation of negatively charged Pt particles which favored the adsorption of n-heptene, a commonly accepted intermediate for n-heptane aromatization. A mechanistic study on the interaction of n-heptene and the Pt clusters with different chemical states based on n-heptene- Temperature Programmed Desorption (TPD) and Density-function theory (DFT) calculations suggested that negatively charged Pt clusters (Ptδ−) were thermodynamically favorable for the adsorption of n-heptene and its further cyclization step.

中国における農民専業合作社法の制定と農産物産地商人の合作社化 : 山東省・青島D果菜専業合作社の事例(中国における農民専業合作社の展開と農産物流通の再編,2010年度大会ミニシンポジウム報告)

中国における農民専業合作社法の制定と農産物産地商人の合作社化 : 山東省・青島D果菜専業合作社の事例(中国における農民専業合作社の展開と農産物流通の再編,2010年度大会ミニシンポジウム報告)

Catalytic upgrading of tars generated in a 100 kWth low temperature circulating fluidized bed gasifier for production of liquid bio-fuels in a polygeneration scheme

Gasification of wheat straw, an agricultural residue with high ash content, was investigated in a low temperature circulating fluidized bed (LT-CFB) gasifier in combination with catalytic tar upgrading as a flexible process to co-produce high quality bio-oil, nutrient rich char, and utilize the producer gas for heat and power production. The change in product distribution and bio-oil quality was studied when conducting the catalytic treatment with HZSM-5/γ-Al2O3 and lower-cost γ-Al2O3. The fuel properties of the raw and upgraded bio-oils were analyzed by elemental composition, moisture, total acid number, size exclusion chromatography, basic nitrogen content, gas chromatography–mass spectrometry with flame ionization detection (GC–MS/FID), 1H nuclear magnetic resonance (NMR), 13C NMR, and two-dimensional heteronuclear single-quantum correlation (2D HSQC) NMR. The operating temperature of the LT-CFB pyrolysis chamber determined the tar yield and quality in the producer gas. With decrease in pyrolysis temperature from 690 to 570 °C, the tar concentration in the producer gas increased, while the higher heating value of the condensed oil phase decreased from ~35 to 30 MJ/kg and the oxygen content, moisture content, and acidity of the bio-oil increased. Both HZSM-5/γ-Al2O3 and γ-Al2O3 were effective catalysts as the tar treatment improved the bio-oil quality in terms of increased heating value and revaporization efficiency, and a reduction in oxygen content, moisture content, total acid number, and basic nitrogen content. Catalytic vapor treatment, e.g. using HZSM-5/γ-Al2O3 at 500 °C, decreased the energy content in the condensed bio-oil slightly from ~22% to ~20%. The oil quality improved significantly, as the oxygen content (water-free) and TAN of the bio-oil decreased from 13 wt% O and 34 mg KOH/g to 11 wt% O and 3 mg KOH/g, respectively. The catalytically treated bio-oils are thus better suited for further processing in existing oil refineries.

Valorization of sewage sludge through catalytic sub- and supercritical water gasification

Sub- and supercritical water gasification is applied to recover energy from sewage sludge in a batch reactor. The effects of reaction temperature and water-soluble additives as catalysts on gasification were examined. The resultant products, including syngas, hydrochar and liquid residues were characterized. The rise of temperature without the presence of catalysts increased the yield of H2 (0.06 (350 °C) to 1.91 mol/kg (450 °C) and enhanced the gasification efficiency (1.29–19.61%), and decreased total organic carbon (TOC) by 68.50% in liquid residue. The changes in product distribution and characteristics of hydrochar and liquid residue implied that the organic matters in sewage sludge were dissolved and hydrolyzed in sub- and supercritical water, resulting in the production of syngas. The catalytic effect of different catalysts in relation to the H2 gas yield was in the following order: KOH > NaOH > Na2CO3 ≈ K2CO3. In the case of catalytic supercritical water gasification at 400 °C, the highest molar fraction (37.28%) and yield of H2 (1.60 mol/kg) were obtained in the presence of KOH. Furthermore, the scanning electron microscopy (SEM) analysis indicated that a conversion and dissolution of the organic matters in sewage sludge to liquid and gas, produced a porous, fragmented structure and disintegrated surface of hydrochar.

Effect of carbon dioxide on thermal treatment of food waste as a sustainable disposal method

Herein, carbon dioxide (CO2) was applied to thermal treatment of real food waste to develop an environmentally benign way to dispose food waste. The food waste used in this study was collected from a food waste treatment plant. The application of CO2 to the thermal treatment of food waste affected the amount of non-condensable gases and condensable compounds produced from the thermal process, while it did not affect the amount of solid residue. When CO2 was supplied during the thermal treatment of food waste, less condensable compounds but more non-condensable gases such as H2, CO, and CH4 were generated during the thermal treatment of food waste at a range of temperatures from 400 to 700 °C. In addition to the change in product distribution, the generation of cyclic compounds was inhibited by applying CO2 to the thermal treatment. For example, approximately 30% less ring-structured compounds (e.g., benzene derivatives) were produced from the thermal treatment at 700 °C in CO2 condition than from the thermal treatment in inert condition. This was likely because CO2 inhibits gas phase free radical addition and/or dehydrogenation of linear compounds. This study suggests that the application of CO2 to thermally treating food waste would help develop a more environmentally friendly food waste treatment method.

Pyrolysis behaviors of coal-related model compounds catalyzed by pyrite

The pyrolysis behaviors of coal-related model compounds (bibenzyl and benzyloxybenzene) were investigated on a fixed-bed reactor catalyzed by pyrite (main component is FeS2). The pyrolysis products were analyzed by gas chromatography (GC). The results indicated pyrite could increase the conversion of the model compounds and the yield of liquid and gas, while decrease the char yield. The theoretical calculation results indicated that the pyrite accelerates the initial bond dissociation of parent molecules, thus the radicals can be produced easily. Moreover, the main reason for the decreased yield of char after adding the pyrite is that the large radicals are stabilized on the surface by adsorption, then having little chance to combine with each other to form char. The changes in pyrolysis product distributions with pyrite were also consistent with the calculation results. When adding tetrahydronaphthalene and pyrite simultaneously, there is a significant synergistic effect, which causing the conversion of bibenzyl increased by 14.78 wt% compared with that adding tetrahydronaphthalene or pyrite alone.

Association with Polyamines and Polypeptides Increases the Relative Yield of 2-Deoxyribonolactone Lesions in Radiation-Damaged DNA.

The production of 2-deoxyribonolactones (C1'-oxidation product), C4'-oxidized abasic sites and C5'-carbonyl terminated strand scission products was investigated in complexes of double-stranded DNA with protamine, poly-L-lysine and spermine exposed to X-ray radiation. The lesions were quantified by high-performance liquid chromatography through the release of the corresponding low-molecular-weight products 5-methylenefuran-2(5H)-one, N-(2'-hydroxy-ethyl)-5-methylene-D3-pyrrolin-2-one and furfural, respectively. All binders were found to increase the relative yield of C1' oxidation up to 40% of the total 2-deoxyribose damage through the indirect effect versus approximately 18% typically found in homogeneous solutions by the same technique. On the contrary, the yield of C5'-oxidation was found to be suppressed almost completely, while in homogeneous solutions it constituted approximately 14% of the total. The observed change in end product distribution is attributed to free valence transfer to and from the complexing agent, although the mechanisms associated with this process remain unclear.

Electrochemical Partial Oxidation of Alkenes: Understanding Selectivity and Reaction Mechanisms

With a deepening electrification of society, electrochemical conversion from one chemical to another will be essential for the chemical plants of the future. While there is intense focus on reduction reactions (i.e. CO2, water, N2), partial oxidation reactions have been relatively underinvestigated. This talk will discuss our recent work on electrochemical partial oxidation of propene. With propene having both a double bond and an allylic carbon, this is an optimal test molecule to create a broad spectrum of products following a variety of mechanisms. By using a Pd catalyst, we were able to produce acrolein, acrylic acid, allyl alcohol, propylene glycol, acetone with only small amounts of CO2 formation. Variations is oxidation potential allowed us to see changes in product distribution, which we then used to theorize potential reaction mechanisms. With acrolein being one of our largest products, this meant the allylic carbon was oxidized rather the double bond. DFT calculations showed that the acrolein mechanism was feasible, provided surface coverage of other species (oxygen species and flat lying propene) dominated the surface coverage, thus allowing for a small amount of allylic carbon to bind to the surface due to steric advantages. Electrochemical Sniffer Chip technology (1) was then used to measure submonolayer gas absorption/desorption as a function of electrochemical potential, which provided supporting evidence to the aforementioned mechanism. The talk will show our process in analyzing this reaction and mechanisms as well as how these discoveries are applicable to the broader field of partial oxidation reactions. (1) Trimarco, D. et. al, Review of Scientific Instruments 86, 075006 (2015) Figure 1

Interrogating Kinetic versus Thermodynamic Topologies of Metal-Organic Frameworks via Combined Transmission Electron Microscopy and X-ray Diffraction Analysis.

Synthetic protocols that preferentially result in metal-organic framework (MOF) crystallization of one topology over another remain an elusive, empirical process. This is primarily because of a lack of fundamental insights into MOF crystal growth and the effect of various experimental parameters on the resulting topologies. In this Communication, we demonstrate the temperature-topology relationship of MOFs constructed from hexanuclear oxozirconium cluster nodes and tetrakis(4-carboxylphenyl)porphyrin linkers via a combined transmission electron microscopy and powder X-ray diffraction study. Synthesis at room temperature led to a mixed phase consisting of 12-connected (assuming no defects)MOF-525 and 6-connected PCN-224, possessing ftw and she topologies, respectively. When the temperature was raised to 145 °C, 8-connected PCN-222 (csq topology) was found, with a possible concurrence of another 8-connected NU-902 (scu topology) and 12-connected PCN-223 (shp topology), in addition to MOF-525 and PCN-224. With an increase in reaction time at 145 °C, a change in product distribution was observed where PCN-222 remained the major crystal phase after 7 days, while the contribution from MOF-525 and PCN-224 decreased. These data suggest that MOF-525 and PCN-224 are the kinetic products while PCN-222 is the thermodynamic product.

Impact of carrier acidity on the conversion of syngas to higher alcohols over zeolite-supported copper-iron catalysts

The development of catalysts showing satisfactory performance to realize a large-scale synthesis of higher alcohols (HA) via CO hydrogenation, which promises higher sustainability compared to current industrial routes, is hindered by limited fundamental understanding. Here, the impact of acidity and porosity of MFI zeolite carriers on the properties of CuFe catalysts was investigated. Significant changes in activity and product distribution were observed at higher concentrations of Brønsted-acid sites over materials featuring similarly sized and distributed metal particles, whereas a hierarchical carrier structure did not produce relevant alterations. Individually feeding methanol, primary and secondary HA, and hydrocarbons over a zeolite with a Si/Al bulk ratio of 40 uncovered that acidity greatly fosters the formation of secondary HA via hydration of the coproduced olefins. Acidic supports are attractive if such products are desired, while are suboptimal to boost HA yields. Indeed, the selectivity to primary HA is concomitantly hindered, since they are partially dehydrated to olefins, which can rehydrate to secondary HA, but mostly undergo coupling reactions followed by hydrogenation and cracking to paraffins, and the CO conversion is lowered. Ion exchange, deposition, and their combination were explored as strategies to add K as a promoter, whereby the second was superior and increased the HA selectivity over the low-acidic CuFe/silicalite from 33 to 43%, while outstandingly minimizing the CO2 selectivity (2%). Finally, it was demonstrated that positive acidity effects can be isolated if a zeolite is used in series to a catalyst producing a high fraction of olefins, since hydration of the latter to secondary HA becomes dominant over other parallel reactions, overall boosting the total HA productivity.