Metal (Mo, W, Ti) Carbide Catalysts: Synthesis and Application as Alternative Catalysts for Dry Reforming of Hydrocarbons-A Review.

Dry reforming of hydrocarbons (DRH) is a pro-environmental method for syngas production. It owes its pro-environmental character to the use of carbon dioxide, which is one of the main greenhouse gases. Currently used nickel catalysts on oxide supports suffer from rapid deactivation due to sintering of active metal particles or the deposition of carbon deposits blocking the flow of gases through the reaction tube. In this view, new alternative catalysts are highly sought after. Transition metal carbides (TMCs) can potentially replace traditional nickel catalysts due to their stability and activity in DR processes. The catalytic activity of carbides results from the synthesis-dependent structural properties of carbides. In this respect, this review presents the most important methods of titanium, molybdenum, and tungsten carbide synthesis and the influence of their properties on activity in catalyzing the reaction of methane with carbon dioxide.

Apparent Kinetics of Co-Gasification of Biomass and Vacuum Gas Oil (VGO).

This communication reports the beneficial effects of co-gasification of biomass and residual oil to produce syngas. In this regard, various blends of glucose (a biomass surrogate) to vacuum gas oil (VGO) have been employed to investigate the synergic effects on the gasification process. The non-isothermal co-gasification experiments were conducted in a thermogravimetric analyzer at different heating rates and gasifying agents. The analysis showed that the co-gasification rate increased with the increase of glucose content in the feedstock. The presence of the oxygen in the biomass molecules helped the overall gasification process. The maximum gasification rate of 42.70 wt/min (DTGmax ) was observed with 25 wt% glucose containing sample. The use of gasifying agents appeared to have some influence, especially during high temperature gasification of the glucose-VGO blends. At a same gasification temperature, the co-gasification rate of glucose-VGO blends were found to be 125.7 wt/min and 98.59 wt%/min for N2 and CO2 , respectively. The kinetics of the co-gasification of glucose-VGO blends was conducted based on modified random pore model using TGA experimental data and implemented in MATLAB. The estimated activation energy and rate constants were found to be consistent to the observed co-gasification rates. The apparent activation energies of co-gasification of VGO/biomass blends with different weight percentages shows values ranging 60.56-48.25 kJ/mol. The kinetics analysis suggested that the addition of biomass helped to increase the reaction rate by lowering the activation energy required for accomplishing the reactions compared with petroleum carbonaceous feedstocks. The reaction rate constants isotherms are plotted to show that the k-values are exhibiting similar trends at moderate heating rates between 20 and 60 °C/min. This remark arises due to the nature of the reactions involved which are considered to be inherently similar in this range of heating rate.

Probing CO Generation through Metal-Assisted Alcohol Dehydrogenation in Metal-2-(arylazo)phenol Complexes Using Isotopic Labeling (Metal = Ru, Ir): Synthesis, Characterization, and Cytotoxicity Studies.

The reaction of 2-{2-(benzo[1,3]dioxol-5-yl)- diazo}-4-methylphenol (HL) with [Ru(PPh3)3Cl2] in ethanol resulted in the carbonylated ruthenium complex [RuL(PPh3)2(CO)] (1), wherein metal-assisted decarbonylation via in situ ethanol dehydrogenation is observed. When the reaction was performed in acetonitrile, however, the complex [RuL(PPh3)2(CH3CN)] (2) was obtained as the main product, probably by trapping of a common intermediate through coordination of CH3CN to the Ru(II) center. The analogous reaction of HL with [Ir(PPh3)3Cl] in ethanol did not result in ethanol decarbonylation and instead gave the organoiridium hydride complex [IrL(PPh3)2(H)] (3). Unambiguous evidence for the generation of CO via ruthenium-assisted ethanol oxidation is provided by the synthesis of the 13C-labeled complex, [Ru(PPh3)2L(13CO)] (1A) using isotopically labeled ethanol, CH313CH2OH. To summarize all the evidence, a ruthenium-assisted mechanistic pathway for the decarbonylation and generation of alkane via alcohol dehydrogenation is proposed. In addition, the in vitro antiproliferative activity of complexes 1-3 was tested against human cervical (HeLa) and human colorectal adenocarcinoma (HT-29) cell lines. Complexes 1-3 showed impressive cytotoxicity against both HeLa (half-maximal inhibitory concentration (IC50) value of 3.84-4.22 µM) and HT-29 cancer cells (IC50 values between 3.3 and 4.5 µM). Moreover, the complexes were comparatively less toxic to noncancerous NIH-3T3 cells.

A [11 C] CO dispensing system for rapid screening of carbonylation reactions.

[11 C] CO is a highly versatile synthon that allows for labeling at carbonyl positions of many molecules by means of transition metal-mediated carbonylation reactions. The intrinsic complexity of carbonylation reactions often requires tedious screening of reaction conditions for obtaining satisfying yields. Herein, a [11 C] CO dispending system for performing multiple reactions with a single batch of cyclotron-produced [11 C]CO2 is described. This semiautomated setup allows for more rapid and efficient screening of reactions and reaction conditions compared with the traditional "one beam for one reaction" strategy.

Last-Step Pd-Mediated [11C]CO Labeling of a Moxestrol-Conjugated o-Iodobenzyl Alcohol: From Model Experiments to in Vivo Positron Emission Tomography Studies.

The fast, efficient, and functional group tolerant last-step radiolabeling of bioconjugates is crucial for positron emission tomography (PET) applications. In this context, o-iodobenzyl alcohol based structures were identified as ideal tags for an easy Pd-catalyzed carbonylation after bioconjugation, and a moxestrol-conjugated precursor was chosen as the model compound for the further studies. Despite scale and time constraints, conditions developed with [12C]CO and [13C]CO were easily transferred to the 11C isotope, and the desired radioactive product was obtained in amounts up to 740 MBq with radiochemical purities higher than 99%. Radio-high-performance liquid chromatography analyses of rat blood samples demonstrated excellent in vivo stability within the time of the acquisition. MicroPET-magnetic resonance imaging showed excretion pathways similar to moxestrol, and molecular modeling was also performed to evaluate the potential ability of this conjugate to bind estrogen receptors α. Thus, being both synthetically and biologically suitable, this strategy clears the path to potential novel biotracers for preclinical PET imaging.

Potassium-Promoted Molybdenum Carbide as a Highly Active and Selective Catalyst for CO2 Conversion to CO.

The high concentration of CO2 bound in seawater represents a significant opportunity to extract and use this CO2 as a C1 feedstock for synthetic fuels. Using an existing process, CO2 and H2 can be concurrently extracted from seawater and then catalytically reacted to produce synthetic fuel. Hydrogenating CO2 directly into liquid hydrocarbons is exceptionally difficult, but by first identifying a catalyst for selective CO production through the reverse water-gas shift (RWGS) reaction, CO can then be hydrogenated to fuel through Fischer-Tropsch (FT) synthesis. Results of this study demonstrate that potassium-promoted molybdenum carbide supported on γ-Al2 O3 (K-Mo2 C/γ-Al2 O3 ) is a low-cost, stable, and highly selective catalyst for RWGS over a wide range of conversions. These findings are supported by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations.

Click and Release: A Chemical Strategy toward Developing Gasotransmitter Prodrugs by Using an Intramolecular Diels-Alder Reaction.

Prodrug strategies have been proven to be a very effective way of addressing delivery problems. Much of the chemistry in prodrug development relies on the ability to mask an appropriate functional group, which can be removed under appropriate conditions. However, developing organic prodrugs of gasotransmitters represent unique challenges. This is especially true with carbon monoxide, which does not have an easy "handle" for bioreversible derivatization. By taking advantage of an intramolecular Diels-Alder reaction, we have developed a prodrug strategy for preparations of organic CO prodrugs that are stable during synthesis and storage, and yet readily release CO with tunable release rates under near physiological conditions. The effectiveness of the CO prodrug system in delivering a sufficient quantity of CO for possible therapeutic applications has been studied using a cell culture anti-inflammatory assay and a colitis animal model. These studies fully demonstrate the proof of concept, and lay a strong foundation for further medicinal chemistry work in developing organic CO prodrugs.

Enhanced charge separation of rutile TiO2 nanorods by trapping holes and transferring electrons for efficient cocatalyst-free photocatalytic conversion of CO2 to fuels.

Modification with chloride and phosphate anions, and coupling with carbon nanotubes could effectively trap holes and transfer the electrons of rutile nanorods, respectively, so as to greatly promote photogenerated charge separation, leading to an obviously-improved cocatalyst-free photocatalytic conversion of CO2 to CH4 and CO, along with the positive effects of constructed phosphate bridges.

CO and CN- syntheses by [FeFe]-hydrogenase maturase HydG are catalytically differentiated events.

The synthesis and assembly of the active site [FeFe] unit of [FeFe]-hydrogenases require at least three maturases. The radical S-adenosyl-l-methionine HydG, the best characterized of these proteins, is responsible for the synthesis of the hydrogenase CO and CN(-) ligands from tyrosine-derived dehydroglycine (DHG). We speculated that CN(-) and the CO precursor (-):CO2H may be generated through an elimination reaction. We tested this hypothesis with both wild type and HydG variants defective in second iron-sulfur cluster coordination by measuring the in vitro production of CO, CN(-), and (-):CO2H-derived formate. We indeed observed formate production under these conditions. We conclude that HydG is a multifunctional enzyme that produces DHG, CN(-), and CO at three well-differentiated catalytic sites. We also speculate that homocysteine, cysteine, or a related ligand could be involved in Fe(CO)x(CN)y transfer to the HydF carrier/scaffold.

Research report: Charcoal type used for hookah smoking influences CO production.

A hookah smoker who was treated for severe carbon monoxide poisoning with hyperbaric oxygen reported using a different type of charcoal prior to hospital admission, i.e., quick-light charcoal. This finding led to a study aimed at determining whether CO production differs between charcoals commonly used for hookah smoking, natural and quick-light. Our hypothesis was that quick-light charcoal produces significantly more CO than natural charcoal. A medium-sized hookah, activated charcoal filter, calibrated syringe, CO gas analyzer and infrared thermometer were assembled in series. A single 9-10 g briquette of either natural or quick-light charcoal was placed atop the hookah bowl and ignited. CO output (ppm) and temperature (degrees C) were measured in three-minute intervals over 90 minutes. The mean CO levels produced by quick-light charcoal over 90 minutes was significantly higher (3728 ± 2028) compared to natural charcoal (1730 ± 501 ppm, p = 0.016). However, the temperature was significantly greater when burning natural charcoal (292 ± 87) compared to quick-light charcoal (247 ± 92 degrees C, p = 0.013). The high levels of CO produced when using quick-light charcoals may be contributing to the increase in reported hospital admissions for severe CO poisoning.

Unusual way of suicide by carbon monoxide. Case Report.

OBJECTIVES: Authors discuss the case of a suicide of a 29-year-old man caused by carbon monoxide (CO) intoxication. What the authors found interesting was the unusual way of committing suicide that required good technical skills and expert knowledge. METHODS: The level of carboxyhemoglobin (COHb) in the blood of the deceased man was routinely determined by the modified method by Blackmoore (1970), using gas chromatography/thermal conductivity detection. The level of saturation of the hemoglobin by CO in the collected blood sample is determined relatively to the same sample saturated to 100%. RESULTS: In the blood sample of the deceased man the lethal concentration of COHb of 76.5% was determined. Within the following examinations the blood alcohol concentration of 0.05 g.kg(-1) was determined. Further analysis revealed traces of sertraline, its metabolite N-desmethylsertraline, omeprazole and caffeine in the liver tissue, traces of N-desmethylsertraline, ibuprofen and caffeine in urine sample, and only traces of caffeine in the stomach content and blood samples were proved. To commit suicide the man used a sophisticated double container-system equipped with a timer for controlled generation of CO based on the chemical reaction of concentrated sulphuric acid and formic acid. The used timer was set by an electromechanical timer switch that triggered the fatal reaction of the acids while the man was sleeping. CONCLUSIONS: The authors discuss an unusual case of suicide by CO intoxication rarely seen in the area of forensic medicine and toxicology that is specific due to its sophisticated way of execution.

Supramolecular assembly promotes the electrocatalytic reduction of carbon dioxide by Re(I) bipyridine catalysts at a lower overpotential.

The addition of methyl acetamidomethyl groups at the 4,4'-positions of a 2,2'-bipyridyl ligand is found to enhance the rate of a bimolecular reduction mechanism of CO2 by Re(I) fac-tricarbonyl chloride complexes. Electrochemical studies, spectroelectrochemical measurements, and molecular dynamics simulations indicate that these methyl acetamidomethyl groups promote the formation of a hydrogen-bonded dimer. This supramolecular complex catalyzes the reductive disproportionation of CO2 to CO and CO3(2-) at a lower overpotential (ca. 250 mV) than the corresponding single-site 2 e(-) reduction of CO2 to CO and H2O catalyzed by the corresponding model complex with a 4,4'-dimethyl-2,2'-bipyridyl ligand. These findings demonstrate that noncovalent self-assembly can modulate the catalytic properties of metal complexes by favoring alternate catalytic pathways.

Selective visible-light-driven CO2 reduction on a p-type dye-sensitized NiO photocathode.

We present a photocathode assembly for the visible-light-driven selective reduction of CO2 to CO at potentials below the thermodynamic equilibrium in the dark. The photoelectrode comprises a porous p-type semiconducting NiO electrode modified with the visible-light-responsive organic dye P1 and the reversible CO2 cycling enzyme carbon monoxide dehydrogenase. The direct electrochemistry of the enzymatic electrocatalyst on NiO shows that in the dark the electrocatalytic behavior is rectified toward CO oxidation, with the reactivity being governed by the carrier availability at the semiconductor-catalyst interface.

Polyoxometalate-mediated electron transfer-oxygen transfer oxidation of cellulose and hemicellulose to synthesis gas.

Terrestrial plants contain ~70% hemicellulose and cellulose that are a significant renewable bioresource with potential as an alternative to petroleum feedstock for carbon-based fuels. The efficient and selective deconstruction of carbohydrates to their basic components, carbon monoxide and hydrogen, so called synthesis gas, is an important key step towards the realization of this potential, because the formation of liquid hydrocarbon fuels from synthesis gas are known technologies. Here we show that by using a polyoxometalate as an electron transfer-oxygen transfer catalyst, carbon monoxide is formed by cleavage of all the carbon-carbon bonds through dehydration of initially formed formic acid. In this oxidation-reduction reaction, the hydrogen atoms are stored on the polyoxometalate as protons and electrons, and can be electrochemically released from the polyoxometalate as hydrogen. Together, synthesis gas is formed. In a hydrogen economy scenario, this method can also be used to convert carbon monoxide to hydrogen.

Studies of cobalt-mediated electrocatalytic CO2 reduction using a redox-active ligand.

The cobalt complex [Co(III)N4H(Br)2](+) (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(7),2,11,13,15-pentaene) was used for electrocatalytic CO2 reduction in wet MeCN with a glassy carbon working electrode. When water was employed as the proton source (10 M in MeCN), CO was produced (fCO= 45% ± 6.4) near the Co(I/0) redox couple for [Co(III)N4H(Br)2](+) (E1/2 = -1.88 V FeCp2(+/0)) with simultaneous H2 evolution (fH2= 30% ± 7.8). Moreover, we successfully demonstrated that the catalytically active species is homogeneous through the use of control experiments and XPS studies of the working glassy-carbon electrodes. As determined by cyclic voltammetry, CO2 catalysis occurred near the formal Co(I/0)redox couple, and attempts were made to isolate the triply reduced compound ("[Co(0)N4H]"). Instead, the doubly reduced ("Co(I)") compounds [CoN4] and [CoN4H(MeCN)](+) were isolated and characterized by X-ray crystallography. Their molecular structures prompted DFT studies to illuminate details regarding their electronic structure. The results indicate that reducing equivalents are stored on the ligand, implicating redox noninnocence in the ligands for H2 evolution and CO2 reduction electrocatalysis.

Suicidal carbon monoxide poisoning by combining formic acid and sulfuric acid within a confined space.

Suicide by inhalation of carbon monoxide produced by mixing formic acid and sulfuric acid within a confined space is a rare method of suicide. This method is similar to the so-called "detergent suicide" method where an acid-based detergent is mixed with a sulfur source to produce hydrogen sulfide. Both methods produce a toxic gas that poses significant hazards for death investigators, first responders and bystanders. Carbon monoxide is an odorless gas, while hydrogen sulfide has a characteristic rotten eggs odor, so the risks associated with carbon monoxide are potentially greater due to lack of an important warning signal. While detergent suicides have become increasingly common in the USA, suicide with formic acid and sulfuric acid is rare with only three prior cases being reported. Greater awareness of this method among death investigators is warranted because of the special risks of accidental intoxication by toxic gas and the possibility that this method of suicide will become more common in the future.

A convenient method to produce [(14) C]carbon monoxide and its application to the radiosynthesis of [carboxyl-(14) C]celivarone, [carboxyl-(14) C]SSR149744.

[carboxyl-(14) C]Celivarone was synthesised from barium [(14) C]carbonate with overall radiochemical yields in the range 49-53%. The synthetic route involves [(14) C]carbonylation methodology, which both decreased the number of synthetic steps and increased the yields obtained from previous synthetic routes.

Ring-shaped Re(I) multinuclear complexes with unique photofunctional properties.

We synthesized for the first time a series of emissive ring-shaped Re(I) complexes (Re-rings) with various numbers of Re(I) units and various lengths of bridge ligands. The photophysical properties of the Re-rings could be varied widely through changes in the size of the central cavity. A smaller central cavity of the Re-rings induced intramolecular π-π interactions between the ligands and consequently caused a stronger emission and a longer lifetime of the excited state. The Re-rings can function as efficient and durable photosensitizers. The combination of a trinuclear Re-ring photosensitizer with fac-[Re(bpy)(CO)3(MeCN)](+) (bpy = 2,2'-bipyridine) as a catalyst photocatalyzed CO2 reduction with the highest quantum yield of 82%.

Self-sufficient and exclusive oxygenation of methane and its source materials with oxygen to methanol via metgas using oxidative bi-reforming.

A combination of complete methane combustion with oxygen of the air coupled with bi-reforming leads to the production of metgas (H2/CO in 2:1 mole ratio) for exclusive methanol synthesis. The newly developed oxidative bi-reforming allows direct oxygenation of methane to methanol in an overall economic and energetically efficient process, leaving very little, if any, carbon footprint or byproducts.

Manganese as a substitute for rhenium in CO2 reduction catalysts: the importance of acids.

Electrocatalytic properties, X-ray crystallographic studies, and infrared spectroelectrochemistry (IR-SEC) of Mn(bpy-tBu)(CO)3Br and [Mn(bpy-tBu)(CO)3(MeCN)](OTf) are reported. Addition of Brönsted acids to CO2-saturated solutions of these Mn complexes and subsequent reduction of the complexes lead to the stable and efficient production of CO from CO2. Unlike the analogous Re catalysts, these Mn catalysts require the addition of Brönsted acids for catalytic turnover. Current densities up to 30 mA/cm(2) were observed during bulk electrolysis using 5 mM Mn(bpy-tBu)(CO)3Br, 1 M 2,2,2-trifluoroethanol, and a glassy carbon working electrode. During bulk electrolysis at -2.2 V vs SCE, a TOF of 340 s(-1) was calculated for Mn(bpy-tBu)(CO)3Br with 1.4 M trifluoroethanol, corresponding to a Faradaic efficiency of 100 ± 15% for the formation of CO from CO2, with no observable production of H2. When compared to the analogous Re catalysts, the Mn catalysts operate at a lower overpotential and exhibit similar catalytic activities. X-ray crystallography of the reduced species, [Mn(bpy-tBu)(CO)3](-), shows a five-coordinate Mn center, similar to its rhenium analogue. Three distinct species were observed in the IR-SEC of Mn(bpy-tBu)(CO)3Br. These were of the parent Mn(bpy-tBu)(CO)3Br complex, the dimer [Mn(bpy-tBu)(CO)3]2, and the [Mn(bpy-tBu)(CO)3](-) anion.