CC Bond Cleavage Research Articles

Iron(II)-catalyzed direct C[sbnd]H cyanoalkylation of 2H-indazoles and coumarins via radical C[sbnd]C bond cleavage

An iron-catalyzed C-3 cyanoalkylation of 2H-indazole and coumarin derivates with cyclobutanone oxime esters has been accomplished, which proceeds efficiently in a high regioselective manner to construct diverse alkylated 2H-indazole and coumarin derivates in moderate to good yields. Preliminary mechanistic studies reveal that a distal cyanosubstituted alkyl radicals intermediate would be formed through radical-involved CC bond cleavage of cyclobutanone oximes ester.

Active sites for the selective hydrodeoxygenation of m-cresol on WOx-modified Pt

Adsorption and reaction of m-cresol on Pt(111) and WOx-modified Pt(111) surfaces was characterized using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and X-ray photoelectron spectroscopy (XPS). The results of this study show that on Pt(111) a strong interaction between the aromatic ring and the Pt surface facilitates CC bond cleavage resulting in decomposition at relatively low temperatures. In contrast, on WOx-modified Pt(111), m-cresol bonds to oxygen vacancy sites on the WOx deposits via the hydroxyl oxygen with the aromatic ring tilted away from the surface, resulting in a bonding configuration that promotes selective CO bond cleavage and limits ring hydrogenation. XPS results also show that interactions at the Pt-WOx interface help stabilize submonolayer WOx deposits in a partially reduced state, thereby maintaining a high concentration of the oxygen vacancy adsorption sites.

Effect of reactive oxygen species on biomass structure in different oxidative processes

Understanding the depolymerization of lignocellulosic biomass with reactive oxygen species provides insight to develop new technologies for the conversion of biomass to fermentable sugars used to produce biofuels. In this study, the effects of four oxidative pretreatment techniques on sugar recovery and lignin degradation of wheat straw were investigated, including potassium superoxide (PS), sodium persulfate (SP), sodium perborate (PB), and iron sulfate-hydrogen peroxide (FE). The pretreated biomass was then characterized in terms of lignin/ash removal, polysaccharide content, sugar recovery, functional group transformations, pyrolysis products, structural modification, and thermal behaviors as compared to untreated biomass. Among the different oxidative pretreatment methods, PS treatment appeared to be the most promising method by increasing glucan recovery from 12.7% (untreated) to 68.9% (treated) and resulting in a 27% decrease of lignin content in the residual wheat straw. FTIR and Py-GC/MS in PS and PB methods confirmed degradation of lignin via oxidative side chain cleavage and syringyl ring oxidation, whereas SP and FE methods only caused oxidative side chain cleavage. Solid-state NMR showed changes in lignin and hemicellulose/cellulose resonances correlating to aliphatic, carbonyl functionality, acetyl groups, and crystalline regions. The thermal behavior of PS-treated wheat straw revealed an increase in cellulose degradation temperature and decreases in activation energy from 259 to 223 kJ/mol compared to raw material. Following PS method (68.9% sugar recovery), SP, PB, and FE methods resulted in recovered sugar of 43.8%, 30.8%, and 28.8%, respectively as compared to 12.7% in the untreated sample. Overall, the results indicate that the aromatic ring side chains and hemicellulose acetyl groups removed by radical fragmentation, polar hydrolysis, and CC bond cleavage play a more important role in sugar recovery than side-chain oxidation.

Catalytic Ru containing Pt3Mn nanocrystals enclosed with high-indexed facets: Surface alloyed Ru makes Pt more active than Ru particles for ethylene glycol oxidation

Tuning the surface property of Pt based nanocrystals at the atomic level is of vital significance to meet superior electrocatalytic performance criteria. In this work, a new strategy to advance fundamental surface study on Pt based nanocrystals is addressed by implanting foreign metals as “active auxiliaries” onto the surface of Pt based nanocrystals to engineer a stable structured catalyst. Under the guidance of this concept, the Ru component was selected as “active auxiliary” to construct Ru containing Pt3Mn catalysts by doping the isolated Ru atoms (Pt3Mn–Ru) and Ru nanoparticles (Pt3Mn@Ru) onto surface layer of Pt3Mn concave nanocubes (CNCs). Strikingly, the Pt3Mn–Ru CNCs showed the most optimal catalytic activity, durability and CO anti-poisoning ability toward ethylene glycol oxidation reaction (EGOR). The specific activity of Pt3Mn–Ru CNCs is 1.32 mA cm−2, which is 1.47 and 3.07 times higher than Pt3Mn@Ru CNCs (0.90 mA cm−2) and pure Pt3Mn CNCs (0.43 mA cm−2). The results of in situ Fourier transform infrared spectroscopy experiments revealed that Pt3Mn–Ru CNCs were more in favor of CC bond cleavage of EG and rapid oxidation/removal of intermediate poisonous COads. Furthermore, the theoretical calculations revealed that the Pt3Mn–Ru CNCs possessed a lower reaction barrier (1.69 eV) for oxidation of COads assisted by adsorbed OHads species, and an energy-favorable position (2.88 Å) for reaction between COads and OHads. This work disclosed a new tactics to develop a novel structured catalyst in possession of excellent electrocatalytic performance, which provided a promising methodology for designing Pt-based nanoparticles as efficient fuel cell catalysts.

Density functional calculations for Rh(I)‐catalyzed C–C bond activation of siloxyvinylcyclopropanes and diazoesters

Density functional theory was employed to investigate rhodium(I)‐catalyzed C–C bond activation of siloxyvinylcyclopropanes and diazoesters. The B3LYP/6‐31G(d,p) level (LANL2DZ(f) for Rh) was used to optimize completely all intermediates and transition states. The computational results revealed that the most favorable pathway was the channel forming the methyl‐branched acyclic product p1 in path A (cyclooctadiene (cod) as the ligand), and the oxidative addition was the rate‐determining step for this channel. It proceeded mainly through the complexation of diazoester to rhodium, rhodium–carbene formation, coordination of siloxyvinylcyclopropane, oxidative addition (C2–C3 bond cleavage) of siloxyvinylcyclopropane, carbene migratory insertion, β‐hydrogen elimination and reductive elimination. The complexation of diazoester to rhodium occurred prior to the coordination of siloxyvinylcyclopropane. Also, the role of the ligands cod, chlorine and 1,4‐dioxane, the effect of di‐rhodium catalyst and the solvent effect are discussed in detail.

Gold nanoparticles stabilized by graphene quantum dots as catalysts for C[sbnd]C bond cleavage in β-O-4 lignin model compounds

In this work, we report oxidative cleavage of CC bonds in β-O-4 lignin models that is catalyzed by gold nanoparticles stabilized by graphene quantum dots (AuNPs-GQDs). We demonstrate that GQDs can enhance the catalytic activity of AuNPs. The AuNPs-GQDs shows the highest catalytic activity when the mass ratio of AuNPs to GQDs is of 1:18. Moreover, AuNPs-GQDs exhibits higher activity in the cleavage of CαCβ bond of the compounds when their Cβ is adjacent to an oxygen atom. The possible oxidation pathway is proposed.

Significantly accelerated PEC degradation of organic pollutant with addition of sulfite and mechanism study

Visible-light-driven photoelectrochemical (PEC) catalysis has been widely studied as a promising technique for the degradation of organic pollutants in wastewater. Herein, we report a sulfite-enhanced PEC degradation process for the degradation of organic pollutant. The degradation rate was significantly enhanced by ～30 times with the addition of 16 mM sulfite. The Electron Spin Resonance (ESR), Transient Absorption (TA) and hole scavenger studies showed that sulfite radicals (SO3 ⦁-) were the main reactive species in the reactions. The pollutant degradation pathway was studied by in-situ techniques and mass spectrometer, showing that the sulfite addition can promote the cleavage of aromatic ring CC bond and CN bond.

Manganese-catalyzed ring-opening carbonylation of cyclobutanol derivatives

Herein, we report a manganese-catalyzed ring-opening carbonylation of cyclobutanol derivatives through cyclic CC bond cleavage. The reaction happens via a radical-mediated pathway to selectively generate 1,5-ketoesters. A variety of substrates with substituents on the aromatic ring reacted with linear alcohols of different chain lengths. Obtained aliphatic esters are very attractive since they are usually difficult to access.

Possible Intermediacy of Cyclopropane Complexes in the Isomerization of Aliphatic Amine Radical Cations.

The isomerization of aliphatic amine radical cations via intermediate [cyclopropane-NH3]+• and [cyclopropane-amine]+• ion-neutral complexes was studied experimentally with double-focusing mass spectrometers and computationally with composite ab initio methods. The results examine and extend Audier's suggestion that primary amine radical cations with alkyl substituents at the β- and/or γ-carbon atoms isomerize via transient complexes of NH3 and alkyl cyclopropanes; these are formed by ring closure of the easily accessible γ-distonic isomers. Ionized amines with substituents at the α-carbon may react analogously when trialkyl cyclopropane complexes can be formed. Isomerization via complex intermediates is a major reaction pathway when the internal energy of the amine radical cation is less than that required for simple CC-bond cleavage. Complexes of unsubstituted or monosubstituted ionized cyclopropanes rarely contribute to the isomerization reactions. Secondary and tertiary amine radical cations do not undergo isomerization via cyclopropane intermediates, whereas aliphatic ether radical cations do.

In situ synthesis of Hägg iron carbide ([formula omitted]) nanoparticles with a high coercivity and saturation magnetization

Magnetic nanoparticles (NPs) suffer from poor magnetic properties (coercivity and saturation magnetization) compare to their bulk. Synthesis of Hägg iron carbide, Fe5C2 magnetic nanoparticles (NPs) was still a challenge for the pure phase and the large-scale production. Herein, a chemical solution route was proposed to obtain pure Fe5C2 phase using amorphous Fe NPs as iron feedstock in presence of Oleylamine (OAm) at elevated temperature. X-ray diffraction results reveal the pure Hägg iron carbide phase for various reaction time from 30 min to 9 h. Fe5C2 NPs show the same morphology as Fe NPs by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Amorphous Fe NPs catalyze the cleavage of CC bonds of OAm at elevated temperature as well act as a template for the in situ nucleation and growth of Fe5C2 NPs. The saturation magnetization of Fe5C2 NPs are 140 emu/g and 123 emu/g for 5 K and 298 K, respectively. The coercive force of Fe5C2 NPs are 452 Oe (298 K) and 703 Oe (5 K), demonstrating the ferromagnetic behavior. The magnetic Fe5C2 NPs showed the high coercivity and saturation magnetization on the nanoscale, revealing the Fe5C2 NPs being a promise candidate for the soft magnetic application such as magnetic medium. This paper presents a convenient procedure to synthesize Hägg iron carbide nanoparticles and may promote its further study in formation mechanism and application such as catalysis.

Visible-light-induced carbosulfonylation of unactivated alkenes via remote heteroaryl and oximino migration

An efficient visible-light photocatalytic protocol for the vicinal heteroarylsulfonylation and oximinosulfonylation of unactivated olefins is described. The addition of sulfonyl radicals to alkenes triggers the intramolecular migration of remote heteroaryl and oximino groups via CC bond cleavage. The transformation features a good functional group tolerance and a broad substrate scope. A variety of valuable heteroaryl- and oximino-substituted alkyl sulfones are obtained under mild conditions in synthetically useful yields.

Ethanol steam reforming with two-stage catalyst system for selective methane production

Ethanol steam reforming over various catalysts was studied to identify the best conditions for selective CH4 production. In the sequence of catalyzed reactions, H2 production was followed by reduction of CO and CO2 to CH4. The compositions of the product gases obtained over Ru/CeO2 and Ru/SiO2 were close to the chemical equilibrium composition at 673 K. However, the product gas compositions obtained over Ru catalysts and Ru-based alloy catalysts were far from the chemical equilibrium composition at 623 K. Ethanol steam reforming by means of a two-stage catalytic process that involved ethanol CC bond cleavage over RuPt/SiO2 and Pd/Al2O3 in the first stage and reduction of CO and CO2 to CH4 over Ru/Al2O3 in the second stage was conducted at 623 K. The product gas compositions obtained over RuPt/SiO2+Ru/Al2O3 and Pd/Al2O3+Ru/Al2O3 were close to the chemical equilibrium composition at 623 K.

Excavated Rh nanobranches boost ethanol electro-oxidation

Direct ethanol fuel cells are a type of promising energy conversion device with high energy density, and their commercialization is still impeded by incomplete oxidation of ethanol on available electrocatalysts. Herein, a kind of novel excavated Rhodium (Rh) nanobranches constructed by ultrathin nanosheets with high-energy {110} facets and high surface area was successfully synthesized, which shows a high selectivity of complete oxidation ethanol to CO2 up to 15.8% (at 0.0 V vs Hg/HgO) in alkaline solution, outperforming currently reported monometallic electro-catalysts. The in situ Fourier transform infrared reflection spectroscopy and density function theory calculations demonstrated that the CC bond cleavage of ethanol is very sensitive to the structure of Rh crystallites, and the unique {110} facets and excavated polyhedral morphology endow the Rh electro-catalysts with unexpected high selectivity, as well as high electro-catalytic activity and great structural stability.

La-mediated dehydrogenation and C[sbnd]C bond cleavage of 1,4-pentadiene and 1-pentyne: Spectroscopy and formation of La(C5H6) and La(C3H4) radicals

La atom reactions with 1,4-pentadiene and 1-pentyne are carried out in a laser-vaporization molecular beam source. Both reactions yield a predominant La(C5H6) radical from ligand dehydrogenation and a minor La(C3H4) species from CC bond cleavage. The metal-hydrocarbon radicals are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species formed by the two reactions are essentially identical and consist of a single vibronic band system for La(C5H6) and two band systems for La(C3H4). Each band system exhibits a strong origin band and several weak vibronic ones. Adiabatic ionization energies, metal-ligand vibrational frequencies, and low-frequency ligand-based modes are measured for the two species. La(C5H6) is identified as a six-membered lanthanacycle [La(CHCHCHCHCH2)] (Iso A, C1), whereas two isomers of La(C3H4) are a four-membered metallacycle La(CHCHCH2) (Iso 1, C1) and a three-membered ring La(CHCCH3) (Iso 2, Cs). The ground electronic state of each radical is a doublet and that of the singly charged cation is a singlet. The remaining two electrons that are associated with the isolated La atom or ion are spin paired in a molecular orbital that is bonding combination between a La 5d orbital and a π* antibonding orbital of the C5H6 or C3H4 fragment. For the 1,4-pentadiene reaction, the formation of the six-membered metallacycle La(C5H6) involves La addition to a C=C double bond, La insertion into two C(sp3)H bonds, and concerted H2 elimination, whereas the formation of the three- and four-membered La(C3H4) rings involves two hydrogen migrations followed by CC bond breakage to eliminate an ethylene molecule. For the 1-pentyne reaction, the formation of each species requires isomerization of a La(1-pentyne) adduct to a La insertion species and then proceeds with the same elemental steps as those for the diene reaction.

High-efficient preparation of gasoline-ranged C5–C6 alkanes from biomass-derived sugar polyols of sorbitol over Ru-MoO3−x/C catalyst

The conversion of biomass-derived sugar polyols to gasoline-ranged bio-fuels requires selective cleavage of CO bond in the reactants to form hydrocarbons by catalytic hydrodeoxygenation (HDO). Generally, Ru metal catalysts exhibit the outstanding hydrogenolysis activity, leading to excessive cleavage of CC and CO bonds, and give large amounts of lower alkanes. In this work, Ru promoted MoO3−x/C catalysts were simply prepared using step impregnation, and successfully applied in the C5–C6 alkane production by the selective CO dissociation of sorbitol in aqueous solution. To screen the optimal reaction conditions, different parameters such as reaction temperature, sorbitol concentration, various transition metals and loading amount of Ru and Mo had been investigated carefully. The experimental results indicated that the Ru-MoO3−x/C catalyst showed the excellent activity with 87.3% yield of C5–C6 alkane and 79.7% yield of C6 alkane on a continuous flow reactor. In addition, the Ru-MoO3−x/C catalyst exhibited superior stability with no observed decrease of activity in 200 h time on stream. Preliminary mechanistic studies supported that the reactions occurred via a selective cleavage of the CO bonds and the synergetic effect of the hydrogenating Ru sites and the active MoO3−x species was the key to such unusual reactivity.

Selective hydrogenation of 1,3-butadiene over single Pt1/Cu(1 1 1) model catalysts: A DFT study

Single atom alloy (SAA) catalyst usually shows high selective hydrogenation properties as compared to that of traditional metal catalyst, but the mechanism is still needed to be understood at the molecular level. The first-principles density functional theory (DFT) calculations were performed to study the selective hydrogenation of 1,3-butadiene into 1-butene catalyzed by sing Pt catalyst [Pt1/Cu(1 1 1) ] as well as high Pt content catalyst [Pt4-line/Cu(1 1 1), i.e. four Pt atoms in a linear type]. The calculation results indicated that the activity of H2 dissociation as well as the H diffusion is facile on both Pt1/Cu(1 1 1) and Pt4-line/Cu(1 1 1) catalysts, which means that the production of H species is not the key factor controlling the selectivity of 1,3-butadiene hydrogenation towards the 1-butene formation. The reaction path calculation results indicated that the kinetic behavior of hydrogenation of 1,3-butadiene to 1-butene is similar for both Pt1/Cu(1 1 1) and Pt4-line/Cu(1 1 1) models, whereas the CH bond scission of 1,3-butadiene displayed a significant difference on these two models, namely it is facile to broke CH bond on Pt4-line/Cu(1 1 1) model, and thus leading to the lower selectivity for the 1-butene formation over Pt4-line/Cu(1 1 1). The reason behind the high activity of CH bond scission on Pt4-line/Cu(1 1 1) comes from the fact that a small deformation energy of 1,3-butadiene molecule occurs on Pt4-line/Cu(1 1 1) surface during the process of CH bond cleavage due to the relatively short CH bond length at transition states as compared with that on Pt1/Cu(1 1 1), and thus resulting in a relatively low CH bond cleavage barrier on Pt4-line/Cu(1 1 1) surface. The present study may help people to design an efficient catalyst for selective hydrogenation of 1,3-butadiene by controlling the activity of CH and/or CC bond cleavage.

High selectivity PtRh/RGO catalysts for ethanol electro-oxidation at low potentials: Enhancing the efficiency of CO2 from alcoholic groups

Conversion the ethanol into CO2 at low potential through CC bond cleavage is vital to further improve the utilization of ethanol in direct ethanol fuel cells. The addition of Rh into Pt lattice is considered as an efficient route to improve the CO2 selectivity during ethanol electro-oxidation. In this work, PtRh alloy nanoparticles with different element ratios supported on reduced graphene oxide (RGO) were synthesized. Among them, Pt1Rh1/RGO shows an ultrahigh mass activity of 0.285 A mgpt−1 at 0.4 V (vs.SCE), 2.48 times as high as that of commercial Pt/C. Results of high-resolution transmission electron microscopy (HRTEM) reveal that the supported Pt1Rh1 alloy nanoparticles are in cubic shape with preferential (100) orientation and high-density of step sites. Results of in-situ FTIR spectra indicate that the addition of Rh greatly alleviates the COad poisoning on Pt surface. CO2 was generated at a low potential of −0.10 V, and the CO2 selectivity is 16.2 times as high as that of commercial Pt/C at 0.40 V. In-situ FTIR spectra using isotopically-labeled ethanol further confirm the superior CO2 selectivity on Pt1Rh1/RGO under low potentials is derived from the addition of Rh and high-density of step sites, which facilitates the CC bond cleavage and the oxidation of alcoholic groups.

Catalytic coal hydrogasification by cobalt-calcium catalyst in a pressurized fluidized bed: Role of hydropyrolysis and catalysis process

Coal pyrolysis, hydropyrolysis and hydrogasification were performed in a lab-scale pressurized fluidized bed with or without cobalt-calcium bimetallic catalyst (Co-Ca) to preliminarily discern the role of hydropyrolysis, Co-Ca catalyst and H2 in the course of coal catalytic hydrogasification (CCHG). The hydrogasification reactivity and chemical structure of the coal chars generated after hydropyrolysis were also analyzed by means of pressurized thermogravimetric analyzer (P-TGA), FT-Raman and FT-IR, etc. Results indicate that Co-Ca catalyst possesses catalytic depolymerization and hydrogenation effect on coal during hydropyrolysis, which resulted in the promoted yield of CH4, tar and the high hydrogasification reactivity of the generated char. Co-Ca catalyst alone and H2 alone are hardly to fracture the CC bonds in condensed aromatic rings of coal, but the union of them yields a superior bonds cleavage ability. The catalytic cleavage of CC bonds is the crucial step of CCHG at the temperature above 800 °C with the hydrogen pressure above 1 MPa. Moreover, the CCHG process over Co-Ca catalyst is discussed and the probable pathways of the catalytic cleavage of CC bonds are proposed.

Faradaic efficiency of ethanol oxidation to CO2 at metallic nanoparticle/short-side-chain PFSA solid-state electrolyte interfaces investigated by on-line DEMS

Ethanol has attracted attention as a renewable fuel for application in electrochemical reformers, for the production of hydrogen, and in fuel cells. The electro-oxidation of ethanol, however, faces a central drawback related to the difficulty for the CC bond cleavage, which is required for its complete electro-oxidation to CO2. Thus, the efficiency has to be increased and this is the main challenge for the use of ethanol as a fuel in such devices. In this study, the ethanol electro-oxidation was studied at metallic nanoparticle/Aquivion® solid-state interfaces. The nanostructured electrocatalysts were formed by Pt/C, Rh/C, Sn/Pt/C, and Sn/(PtRh)/C nanoparticles, and the electrocatalysis was tested at temperatures ranging from 25 to 140 °C. Potentiostatic and potentiodynamic measurements showed a marked effect of the temperature on the electrocatalytic activity and, principally, on the stability, due to lower poisoning by adsorbed reaction intermediates above 100 °C. By using a new setup for coupling the solid-state electrolyte cell with a DEMS (Differential Electrochemical Mass Spectrometry) equipment, with a proper calibration, it was possible to determinate the faradaic efficiency of ethanol electrochemical oxidation to CO2 at each studied condition. The results showed that the CO2 current efficiencies (CCE) increased from approximately zero, at 25 °C, to 54.0, 44.1, 22.7, and 13.1% for Rh/C, Pt/C, Sn/(PtRh)/C (1:3), and Sn/Pt/C (1:3), respectively, at 120 °C, under potentiostatic conditions. The impact of the temperature was more prominent for Rh/C, and this was associated to its ability for ethanol dehydrogenation in the methyl group, resulting in the formation of adsorbed oxametallacycle species, that facilitates the direct cleavage of the CC bond, this step being more rapid at 120 °C than at ambient temperature.

In-situ probing photocatalytic C[sbnd]C bond cleavage in ethylene glycol under ambient conditions and the effect of metal cocatalyst

Photocatalytic polyol conversion provides a green approach for the synthesis of value-added products. However, efficient and selective photocatalysts that can prevent unwanted full oxidation are still missing, mostly due to a lack of mechanistic understanding. Here we use ethylene glycol (EG) as model compound to study the reaction pathways in photocatalytic polyol dissociation under aerated conditions using in-situ vibrational spectroscopy coupled with mass spectrometry. On pristine TiO2, the presence of oxygen leads to the formation of formaldehyde via photocatalytic CC bond cleavage, where the removal of photo-generated surface adsorbed proton (Hads+) in the form of water is the rate determining step (RDS). The photo-generated formaldehyde molecules subsequently convert into CO2via complete oxidation by oxygen, or into paraformaldehyde by polymerization with water. A promotion effect is observed when noble metal (Au, Pt, Ag) nanoparticles (NPs) are used as cocatalysts. While Ag and Au selectively promote the formation of paraformaldehyde, the addition of Pt facilitates the complete oxidation of EG into CO2. By performing the reaction under a low oxygen partial pressure, we rationalize that Ag and Au NPs accelerate the polymerization of formaldehyde by providing water rapidly through direct oxidation of Hads oxidation, whereas Pt NPs supply water indirectly, in a pathway via H2 or formaldehyde oxidation.