A DFT study of methane activation on graphite surfaces with vacancy defects

The activation of methane on graphite surfaces with monovacancies and 5-8-5 vacancies have been investigated using density functional theory. Sixteen different initial adsorption configurations were investigated to identify the most favorable activation site. It is found that methane tends to be activated on the defective graphite surfaces, and the most stable configuration is that methane activation happened in the center hole of the monovacancy site, with a reaction energy of 1.13 eV. Electron transfer and weaker electrostatic potential of the vacancy region indicate that carbon atom of methane tends to fill the vacancy and makes the system more stable.

Methane activation by[LnO]^(+):the 4f orbital matters

Gas-phase reactions of[LnO]^(+)with methane have been studied by using inductively coupled plasma-mass spectrometer(ICP-MS)combined with quantum chemical calculations.Experiments indicate that the[LnO]^(+)(Ln=Sm-Lu)ions are able to activate methane to generate methyl radicals.In particular,[EuO]^(+)and[YbO]^(+)exhibit the highest reactivity.Interestingly,ab initio computations reveal a novel HAT process operating in the absence of a terminal oxygen radical,as mediated by[EuO]^(+)and[YbO]^(+).Such a process diverges from previous findings on the methane activation by metal oxide clusters,not only on the electronic pattern during the course of hydrogen transfer,but also on the important role that 4f electrons play.The associated electronic origins have been discussed,and the well-designed 4f electron occupation may turn to be a promising approach in constructing lanthanide involved catalysts.

NOX -Catalyzed Gas-Phase Activation of Methane: the Formation of Hydrogen

NO_x-catalyzed oxidation of methane without a solid catalyst wasinvestigated, and a hydrogen selectivity of 27% was obtained with an overall methane conversion of34% and a free O_2 concentration of 1.7% at 700℃.

Screening performance of methane activation over atomically dispersed metal catalysts on defective boron nitride monolayers:A density functional theory study

Methane(CH_(4))controllable activation is the key process for CH_(4)upgrading,which is sensitive to the surface oxygen species.The high thermal conductivity and superb thermal stability of the hexagonal boron nitride(h-BN)sheet makes a single transition metal atom doped hexagonal boron nitride monolayer(TM-BN)possible to be a promising material for catalyzing methane partial oxidation.The performances of 24 TM-BNs for CH_(4)activation are systematically investigated during the CH_(4)oxidation by means of first-principles computation.The calculation results unravel the periodic va riation trends for the stability of TM-BN,the adsorption strength and the kind of O_(2)species,and the resulting CH_(4)activation performance on TM-BNs.The formed peroxide O_(2)^(2-)of which the O-O bond could be broken and O-anions are found to be reactive oxygen species for CH_(4)activation under the mild conditions.It is found that the redox potential of TM center,including its valence electron number,coordination environment,and the work function of TM-BN,is the underlying reason for the formation of different oxygen species and the resulting activity for CH_(4)oxidative dehydrogenation.

Direct experimental detection of hydrogen radicals in non-oxidative methane catalytic reaction

Non-oxidative conversion of methane to olefins,aromatics and hydrogen(MTOAH) has been reported recently over metal single sites such as iron and platinum.The reaction was proposed to involve catalytic activation of methane followed by gas phase C-C coupling of methyl radicals.This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species(denoted as Fe-reactor).Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2(ethane,ethylene and acetylene) and 31.8% toward BTX(benzene,toluene and xylene),respectively.The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene,which provides an additional route of methane activation apart from catalytic activation.

On the Role of Vanadia Species for VO_(x)/SiO_(2) in the Selective Oxidation of Methane

Various VO_x/SiO_2 catalysts were prepared by the methods of physical mixing,conventional wetness impregnation and ultrasonication-assistant impregnation. The catalysts werecharacterized by XRD, UV-Vis DRS, Raman, TPR, ESR and TPSR techniques and the nature of the vanadiumspecies were correlated to their catalytic performance in the reaction of direct conversion ofmethane to formaldehyde. It is concluded that highly dispersed monomeric and low oligomeric vanadiaspecies are formed on the sample prepared with both traditional wetness impregnation method andultrasonication-assistant impregnation, whereas in the latter case, the amount of oligomeric vanadiaspecies is much smaller. The V_2O_5 microcrystallines are the dominant species on the materialprepared by physical mixing method. During the selective oxidation of methane, V^V species arereduced to V^(IV) paramagnetic species and both microcrystalline V_2O_5 species and oligomericvanadia species are found to further disperse and transform into tetrahedral vanadia species. Basedon the results of UV Raman spectroscopy and TPSR, CO_2 is suggested to be formed via two differentroutes, in which one is from the sequence reaction of CH_4 → HCHO → CO → CO_2 over monomericvanadia species, and the other is from the direct oxidation of methane to CO_2 over oligomericvanadia species. Oligomeric vanadia species is more active than monomeric vanadia species formethane activation.

DFT Study on the Germanium Ion Activated C–H Bond in Methane

Thermal reactions of methane with the main group metal cations Ge＋,GeO＋,GeOH＋ and OGeOH＋ were investigated by state-of-the-art quantum chemical calculations.For GeO＋/CH_4,a H atom in CH_4 abstracted by the O atom in GeO＋ to form GeOH＋ and CH_3˙constitutes the channel mainly.The barrier-free process,combined with a large exothermicity,suggested a fast and efficient reaction in agreement with the experiment.For OGeOH＋ and CH_4,the intermediates and products of the most favorable path were below the reactant asymptote,and the reaction was easy to take place,while for Ge＋ and GeOH＋,the activation of C-H bond in methane was hard to happen under ambient temperature.The results showed,in contrast to the inertness of Ge~＋ and Ge OH＋,the GeO＋ and OGeOH＋ can activate the H_3C-H bond.The NBO natural charge and molecular electrostatic potential were used to analyze the four main group metal germanium constructions.The phenomenon suggested that ligands affect the electronic character and tune the chemical features of metal germanium center.

Widespread Methane Seep Activities along the Western Slope of the Okinawa Trough, East China Sea

The westem slope of the Okinawa trough has been considered to experience important methane seep activities. Abundant terrigenous sediments supply and widely developed normal faults make this area an ideal place for methane production, methane fluids migration and associated anaerobic oxidation of methane.

Co-aromatization of methane and hexane over Pt encapsulated in ZSM-5 zeolite and the electronic effect of K promoters

The co-aromatization of methane with higher hydrocarbons represents a promising route to valorize methane, an abundant but underexploited carbon resource. In this study, we elucidate a novel approach to enhance the catalytic co-aromatization of hexane and methane by confining Pt within zeolite catalysts and modulating its electron density. Our findings show that encapsulating Pt within MFI structure is pivotal for activating the feedstock and fostering the formation of aromatic products. Interaction between K atoms and the silanol nest forms siloxy groups which are critical for the stabilization of Pt species. Tuning the K content in PtSn@MFI catalysts adeptly alters the electronic configuration of Pt clusters. This modification is corroborated by infrared and X-ray photoelectron spectroscopy analysis, and density functional theory calculations. Remarkably, the catalyst with 0.8 wt% K exhibits an optimal Pt electron density, driving its superior efficacy in the co-aromatization reaction, converting 0.78 mol of methane for each mole of hexane processed. By employing ~(13)C isotopic labeling and solid-state NMR studies, we demonstrate the participation of methane in the adsorbed species inside the zeolite channel and its incorporation to the benzyl site of the substitute group and phenyl rings in aromatic compounds, underscoring the importance of Pt encapsulation.

Emerging importance of shale gas to both the energy & chemicals landscape

This perspectives article is intended highlight the growing importance and emergence of shale gas as an energy resource and as a source of chemicals. Over the next decades huge amounts of newly discovered deposits of trapped gas are expected to be produced not only in the USA but elsewhere providing a wealth of methane and ethane not only used for energy production, but also for conversion to lower hydrocarbon chemicals. This manuscript seeks to focus on the potential of trapped natural gas around the world. The potential new volumes of trapped gas within shale or other mineral strata coming to the marketplace offer a tremendous opportunity if scientists can invent new, cost effective ways to convert this methane to higher value chemicals. Understanding how to selectively break a single C-H bond in methane while minimizing methane conversion to C02 is critical.

A new process to improve short-chain fatty acids and bio-methane generation from waste activated sludge

As an important intermediate product, short-chain fatty acids（SCFAs） can be generated after hydrolysis and acidification from waste activated sludge, and then can be transformed to methane during anaerobic digestion process. In order to obtain more SCFA and methane,most studies in literatures were centered on enhancing the hydrolysis of sludge anaerobic digestion which was proved as un-efficient. Though the alkaline pretreatment in our previous study increased both the hydrolysis and acidification processes, it had a vast chemical cost which was considered uneconomical. In this paper, a low energy consumption pretreatment method, i.e. enhanced the whole three stages of the anaerobic fermentation processes at the same time, was reported, by which hydrolysis and acidification were both enhanced, and the SCFA and methane generation can be significantly improved with a small quantity of chemical input. Firstly, the effect of different pretreated temperatures and pretreatment time on sludge hydrolyzation was compared. It was found that sludge pretreated at 100°C for 60 min can achieve the maximal hydrolyzation. Further, effects of different initial p Hs on acidification of the thermal pretreated sludge were investigated and the highest SCFA was observed at initial p H 9.0with fermentation time of 6 d, the production of which was 348.63 mg COD/g VSS（6.8 times higher than the blank test） and the acetic acid was dominant acid. Then, the mechanisms for this new pretreatment significantly improving SCFA production were discussed. Finally,the effect of this low energy consumption pretreatment on methane generation was investigated.