Dissociation Of CH Research Articles

Formation and Dissociation of CH4 and CO2 Hydrates in Presence of a Sediment Composed by Pure Quartz Mixed with Ti23 Particles.

The present research deals with the formation and dissociation of methane and carbon dioxide hydrates in a confined environment (small—size reactor) and in presence of a porous sediment of pure quartz impregnated with Ti23 particles. This research is part of a wider study aimed at verifying the possibility to use metallic powders, produced via gas-atomization for applications in additive manufacturing, as additives during the production/dissociation of gas hydrates. The porous medium was used to ensure the presence of Ti23 particles in the whole volume and not only in the lowest portion of the internal volume. For both the guest compounds considered, two Ti23 concentrations were explored, respectively, 8.68 and 26.04 wt%. Under the thermodynamic point of view, the dissociation process well approximated the phase equilibrium (defined with values collected from literature) for both compounds. In addition, the amount of gas trapped into hydrates, evaluated as a function of the initial amount of gas inserted inside the reactor, did not show relevant changes. Conversely, the presence of Ti23 was found to reduce the induction time for both components, thus allowing to define it as a kinetic promoter for the process. Such tendency was found to increase with the concentration.

Computational design of BC3N2 based single atom catalyst for dramatic activation of inert CO2 and CH4 gasses into CH3COOH with ultralow CH4 dissociation barrier

The production of CH3COOH from CO2 and CH4 has stimulated much interest due to the high energy density of C2 species. Various kinds of catalysts have been developed while the high dissociation barrier of CH4 and low selectivity still hinders the efficiency of the reaction. We have herein proposed a novel catalyst with single metals loaded on 2D BC3N2 substrate (M@2D-BC3N2) based on density functional theory. Among numerous candidates, Pt@2D-BC3N2 possesses the most favorable reactivity with an ultralow barrier of CH4 splitting (0.26 eV), which is due to the efficient capture ability of CH4 on Pt site. Besides, the selectivity for CH3COOH is also very high, which mainly stems from the unique electronic properties of molecules and substrate: The degenerated states, including s, px, py and pz, in CO2 reflects the existence of delocalized π bonds between C and O. This can interact with states of Pt(s), Pt(pz), Pt(dxz), Pt(dyz),and Pt(z2) in Pt@2D-BC3N2. The kinetics model also proves that our system can promote CH3COOH production via simply increasing the temperature or the coverage of CH4 and CO2. Our results provide a reasonable illustration in clarifying mechanism and propose promising candidates with high reactivity for further study.

Ni/Ce0.9Eu0.1O1.95 with enhanced coke resistance for dry reforming of methane

Methane reforming with carbon dioxide provides an environmentally friendly route for converting methane to synthesis gas while consuming two greenhouse gases. Large-scale implementation of this process has been stalled by the lack of stable catalysts owing to the rapid deactivation caused by carbon deposition and sintering. Ni/Ce0.9Eu0.1O1.95 catalysts with better activity and enhanced stability are synthesized for dry reforming of methane. This reaction is believed to occur via the direct C-H bond dissociation of CH4 to form surface carbon intermediates on metal sites followed by the oxidation of carbon intermediates to CO. Compared with CeO2, Ce0.9Eu0.1O1.95 with stronger lattice oxygen mobility and higher oxygen storage capacity generates more mobile active oxygen species that participate in eliminating the carbon deposition. Moreover, the particle size of Ni species decreases and Ni shifts to higher oxidation state as a result of the strong metal-support interaction over Ce0.9Eu0.1O1.95. The more surface oxygen species are involved in the reaction, the more methane can be converted to CO rather than surface carbon. As a consequence, the balance between the rate of carbon generation (i.e., the direct C-H bond dissociation of CH4) and the rate of carbon consumption (i.e., the oxidation of formed carbon intermediates) can be achieved for dry reforming of methane over Ni/Ce0.9Eu0.1O1.95, leading to less coke accumulation and thereafter an improved overall catalytic performance.

A Novel Synergetic Effect Between Ru and CeO2 Nanoparticles Leads to Highly Efficient Photothermocatalytic CO2 Reduction by CH4 with Excellent Coking Resistance

Highly efficient photothermocatalytic CO2 reduction by CH4 (CRM) on Ru/CeO2 is realized by merely using focused UV–vis–IR irradiation. It shows very high production rates of H2 and CO (57.37 and 65.79 mmol min−1 g−1), and a large light‐to‐fuel efficiency (30.6%), much higher than those of Ru/Al2O3. It also shows good catalytic durability and excellent coking resistance with an extremely low coke formation rate (rC), 30.6 times lower than that of Ru/Al2O3. This is attributed to a synergetic effect between Ru and CeO2 nanoparticles. The formation of a Ru/CeO2 interface promotes CH4 dissociation on Ru nanoparticles. The produced carbon species is not only oxidized by the oxygen produced by CO2 dissociation on Ru nanoparticles like Ru/Al2O3, but also by the active oxygen of CeO2. CO2 molecules strongly adsorb on the resultant oxygen vacancies of CeO2, forming a CO2 molecule fence around Ru nanoparticles, accelerate the oxidation of carbon species, thus improving catalytic activity and tremendously reducing rC. The photothermocatalytic CRM on Ru/CeO2 follows a light‐driven thermocatalysis mechanism. A novel photoactivation is found to enhance the catalytic activity due to both CH4 dissociation and the oxidation of carbon species being promoted upon light irradiation.

Characterization of plasma catalytic decomposition of methane: role of atomic O and reaction mechanism

In this work, we investigated atmospheric pressure plasma jet (APPJ)-assisted methane oxidation over a Ni-SiO2/Al2O3 catalyst. We evaluated possible reaction mechanisms by analyzing the correlation of gas phase, surface and plasma-produced species. Plasma feed gas compositions, plasma powers, and catalyst temperatures were varied to expand the experimental parameters. Real-time Fourier-transform infrared spectroscopy was applied to quantify gas phase species from the reactions. The reactive incident fluxes generated by plasma were measured by molecular beam mass spectroscopy using an identical APPJ operating at the same conditions. A strong correlation of the quantified fluxes of plasma-produced atomic oxygen with that of CH4 consumption, and CO and CO2 formation implies that O atoms play an essential role in CH4 oxidation for the investigated conditions. With the integration of APPJ, the apparent activation energy was lowered and a synergistic effect of 30% was observed. We also performed in-situ diffuse reflectance infrared Fourier-transform spectroscopy to analyze the catalyst surface. The surface analysis showed that surface CO abundance mirrored the surface coverage of CH n at 25 °C. This suggests that CH n adsorbed on the catalyst surface as an intermediate species that was subsequently transformed into surface CO. We observed very little surface CH n absorbance at 500 °C, while a ten-fold increase of surface CO and stronger CO2 absorption were seen. This indicates that for a nickel catalyst at 500 °C, the dissociation of CH4 to CH n may be the rate-determining step in the plasma-assisted CH4 oxidation for our conditions. We also found the CO vibrational frequency changes from 2143 cm−1 for gas phase CO to 2196 cm−1 for CO on a 25 °C catalyst surface, whereas the frequency of CO on a 500 °C catalyst was 2188 cm−1. The change in CO vibrational frequency may be related to the oxidation of the catalyst.

Role of hydrogen in the dissociation of CH4 on different graphene by DFT study

The effect of hydrogen on the growth mechanism of pyrocarbon has attracted much attention. The influence of hydrogen on the dissociation from CH4 to C2H2 on pristine graphene, N-doped graphene and vacancy graphene have been investigated by using density functional theory. There are two kinds of heterogeneous reaction pathways when the hydrogen is involved, i.e., dehydrogenation reactions and H-abstraction reactions. The transition state calculations were performed to acquire the reaction pathways on each substrate after obtaining the most stable adsorption configurations of the reactants and products. The results indicate that the adsorptions of reactants are not affected by hydrogen. The dehydrogenation reactions are more favored on vacancy graphene, and the H-abstraction reactions are more favored on the pristine graphene and N-doped graphene. The dehydrogenation reactions on the vacancy graphene are most favored among all these reactions in favor of the deposition of pyrocarbon. The dehydrogenation reactions on these three substrates are affected by hydrogen.

Controlling carbon formation over Ni/CeO2 catalyst for dry reforming of CH4 by tuning Ni crystallite size and oxygen vacancies of the support

This work investigates the effect of Ni crystallite size and oxygen vacancies of the support on the formation of carbon over Ni/CeO2 catalysts for dry reforming of methane at 1073 K. A large crystallite size variation is achieved by using different Ni loading (5 and 10 wt%) and calcination temperatures (673, 873, 1073 and 1473 K). In situ XRD and XANES experiments reveal that the increase in calcination temperature increases the Ni crystallite size, whereas the amount of oxygen vacancies decreases. The amount of carbon formed during DRM increases as Ni crystallite size increases, achieving a maximum at around 20−30 nm and then, it continuously decreases. However, carbon deposition is negligeable below 10 nm and above 100 nm. For the catalysts with very large Ni crystallite sizes, the CH4 dissociation rate is likely so low that carbon species formed reacts and carbon accumulation does not take place. However, the oxygen vacancies of ceria do not contribute to the carbon removal from the Ni surface due to the low metal-support interface on these large Ni particles.

Mode selective chemistry for the dissociation of methane on efficient Ni/Pt-bimetallic alloy catalysts.

The mode selectivity of methane dissociation is studied on three different Ni/Pt-bimetallic alloy surfaces using a fully quantum approach based on reaction path Hamiltonian. Dissociative sticking probability depends on the composition of alloying metals, excited vibrational mode, and symmetry of the reaction path about the plane perpendicular to the catalyst surface containing the carbon atom and two hydrogen atoms. Our calculations show that symmetry of the minimum energy reaction path depends on the surface alloy composition. In the transition state, the dissociating C-H bond elongates significantly for the dissociation of methane on these alloy systems. A significant decrease in the frequency of the symmetric stretching mode and the two bending modes near the transition state is observed on all the alloy surfaces. Under the vibrational adiabatic limit, excitation of these softened modes enhanced the dissociation probability compared to the ground vibrational state. The reaction probability values decrease abruptly at the incident energies less than the zero-point energy corrected barrier height. With the inclusion of non-adiabatic vibrational coupling terms, reaction probability in the low incident energy region increases to a greater extent, and mode selective behavior also becomes different from that observed within the vibrational adiabatic limit. Symmetric stretching mode displayed the highest reactivity on all the alloy surfaces. Overall, Ni8/Pt(111) is found to be the most reactive toward the methane dissociation.

Dry reforming of methane on Ni(1 1 1) surface with different Mo doping ratio: DFT-assisted microkinetic study

Ni-based catalysts are one of the most promising Dry Reforming reaction (DRM) catalysts due to their cheapness and high catalytic activity, but the deactivation caused by severe carbon deposition is a common problem in Ni-based catalysts, and one solution is to dope with other elements. In this paper, density functional theory (DFT) combined with microkinetic simulation was used to study the effect of the surface doping concentration of Mo on the catalytic activity and carbon deposition resistance of Ni catalyst. In the surface doping model, the Mo surface doping concentration is set to 0, 1/9, 2/9, 3/9, 4/9 ML, namely Ni(111), NiMo1(111), NiMo2(111), NiMo3(111) and NiMo4(111). The electronic structure analysis shows that the doping of Mo improves the electron donating ability of the Ni catalyst and therefore generally increases the adsorption energy of the intermediate species in the DRM reaction. Compared with Ni(111), on NiMox(111)(x = 1–3), the activation energy of CH4 dissociation, the activation energy of CO2 dissociation, and the activation energy of C-O bond formation are generally reduced, while the activation energy of CH* dissociation and CHxO(x = 1–2) dehydrogenation increases. It was shown that the CH-O oxidation route is favorable for DRM and the Mo doped Ni catalyst showed lower free energy span. These DFT results clearly show the doping Mo not only improve the DRM catalytic activity but also enhance the carbon resistance ability. In the microkinetic model, the reaction sites on the catalyst surface were distinguished into sites affected by Mo (#) and sites not affected by Mo (*), and the influence of O coverage was considered on the activation energy of CO2 dissociation at the reaction sites affected by Mo. At 1073.15 K, the order of the catalytic activity of these catalysts for DRM reaction is NiMo2(111) > NiMo3(111) > NiMo1(111) > Ni(111), and NiMo2(111) shows the best catalytic activity for DRM. The microkinetic simulation results showed that without considering that adsorbed O may lead to the formation of NiMoO4 and thus affect the catalytic activity, the Mo-doped Ni catalyst, especially NiMo2(111), exhibits much higher catalytic activity than Ni(111) under high temperature conditions, and Ni(111) is mainly occupied by C* whereas NiMox(111)(x = 1–3) is basically not affected by C species when the simulation reaches a steady state. The strong electron donating ability of Mo is considered to be the basis for increasing the catalytic performance of Ni-based catalysts, which means that our conclusion can be more widely promoted, i.e. the catalytic activity and carbon deposition resistance of Ni-based catalysts can be improved by doping trace metals with strong electron donating ability.

Photodissociation of o-xylene at 266 nm: imaging the CH3 dissociation channel

Photodissociation of o-xylene at 266 nm: imaging the CH3 dissociation channel

Rationalization of Nonlinear Adsorption Energy-Strain Relations and Brønsted-Evans-Polanyi and Transition State Scaling Relationships under Strain.

Scaling relations play a vital role in high-throughput screening of catalytic materials, and more and more attention is being paid to strain-based regulation of catalytic performance. Here we investigated the variation of several energetics, including adsorption energies in the initial state, transition state, and final state, reaction energies, and energy barriers with strain, by studying CO, BH, NH, CH, and NO adsorption and dissociation on M(111) (M = Cu, Ag, Ni, Pd, or Pt) surfaces. We show that energy barriers, reaction energies, and adsorption energies can vary either linearly or nonlinearly (quadratically) with strain. Systems with stronger adsorbate-substrate interaction and weaker atom-atom interaction in substrates are more likely to exhibit nonlinear relations. The well-known Brønsted-Evans-Polanyi relationships and transition state scaling relationships under strain were also examined, and both of them can be nonlinear under strain, in principle. The observed nonlinear relationships were satisfactorily rationalized with the equations derived from Mechanics of Solids.

Insight into the anti-coking ability of NiM/SiO2 (M=ZrO2, Ru) catalyst for dry reforming of CH4 to syngas

The development of Ni-based catalysts with outstanding anti-coking ability is necessary for realizing the industrial application of dry reforming of CH4 (DRM) to syngas. Here, a facile combustion method with unique characteristic was employed to prepare the Ni/SiO2 catalyst with different promoters (ZrO2 or Ru). The effects of Ni particle size and promoter (ZrO2 or Ru) on the anti-coking ability of Ni/SiO2 catalyst were examined. The XRD and TEM results showed that improved Ni dispersion can be obtained via the facile combustion method, accompanying with enhanced metal-support interaction and CO2 adsorption capacity confirmed by H2-TPR and CO2-TPD, respectively. In comparison with Ni-IMP catalyst (prepared via the traditional impregnation method), the carbon deposition over Ni–C catalyst (prepared via the combustion method) decreased by 67% (from 2.7 to 0.9 mg carbon deposition·g−1CH4) as a result of the small Ni particles. The H2-TPR and XPS results revealed the interaction between promoter (ZrO2 and Ru) and Ni. The addition of ZrO2 can enhanced the CO2 activation ability of catalyst and the formed oxygen species can facilitate the elimination of carbon species, further decreasing the carbon deposition compared with Ni–C catalyst. The best catalytic performance with least carbon deposition (only 0.4 mg carbon deposition·g−1CH4) is achieved on the NiRu–C catalyst. The slower CH4 dissociation rate and the improved CO2 activation benefited from Ru can bring in the better balance between the carbon formation and elimination, leading to the best anti-coking ability of catalyst.

Rhodium Indenyl NHC and Fluorenyl-Tethered NHC Half-Sandwich Complexes: Synthesis, Structures and Applications in the Catalytic C-H Borylation of Arenes and Alkanes.

Indenyl (Ind) rhodium N‐heterocyclic carbene (NHC) complexes [Rh(η 5‐Ind)(NHC)(L)] were synthesised for 1,3‐bis(2,6‐diisopropylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene (SIPr) with L=C2H4 (1), CO (2 a) and cyclooctene (COE; 3), for 1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene (SIMes) with L=CO (2 b) and COE (4), and 1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene (IMes) with L=CO (2 c) and COE (5). Reaction of SIPr with [Rh(Cp*)(C2H4)2] did not give the desired SIPr complex, thus demonstrating the “indenyl effect” in the synthesis of 1. Oxidative addition of HSi(OEt)3 to 3 proceeded under mild conditions to give the Rh silyl hydride complex [Rh(Ind){Si(OEt)3}(H)(SIPr)] (6) with loss of COE. Tethered‐fluorenyl NHC rhodium complexes [Rh{(η 5‐C13H8)C2H4N(C)C2H x NR}(L)] (x=4, R=Dipp, L=C2H4: 11; L=COE: 12; L=CO: 13; R=Mes, L=COE: 14; L=CO: 15; x=2, R=Me, L=COE: 16; L=CO: 17) were synthesised in low yields (5–31 %) in comparison to good yields for the monodentate complexes (49–79 %). Compounds 3 and 1, which contain labile alkene ligands, were successful catalysts for the catalytic borylation of benzene with B2pin2 (Bpin=pinacolboronate, 97 and 93 % PhBpin respectively with 5 mol % catalyst, 24 h, 80 °C), with SIPr giving a more active catalyst than SIMes or IMes. Fluorenyl‐tethered NHC complexes were much less active as borylation catalysts, and the carbonyl complexes were inactive. The borylation of toluene, biphenyl, anisole and diphenyl ether proceeded to give meta substitutions as the major product, with smaller amounts of para substitution and almost no ortho product. The borylation of octane and decane with B2pin2 at 120 and 140 °C, respectively, was monitored by 11B NMR spectroscopy, which showed high conversions into octyl and decylBpin over 4–7 days, thus demonstrating catalysed sp3 C−H borylation with new piano stool rhodium indenyl complexes. Irradiation of the monodentate complexes with 400 or 420 nm light confirmed the ready dissociation of C2H4 and COE ligands, whereas CO complexes were inert. Evidence for C−H bond activation in the alkyl groups of the NHC ligands was obtained.

Stabilizing Ni-Co Alloy on Bimodal Mesoporous Alumina to Enhance Carbon Resistance for Dry Reforming of Methane

Alloying nickel with a transition metal and further stabilizing an active metal on bimodal support are regarded as a promising strategy to improve carbon resistance for dry reforming of methane (DRM) reaction. In this work, a bimodal mesoporous alumina-supported Ni-Co alloy catalyst (NiCo/MMAl) was prepared via the evaporation-induced self-assembly method and employed to catalyze DRM reaction. The promotive effect of Ni-Co alloy with a bimodal porous structure on the carbon resistance was investigated. The presence of Ni-Co alloy was confirmed on porous alumina. The NiCo/MMAl catalyst possessed two porous structures, a small-sized mesopore at 10 nm and a large-sized one at 40 nm. NiCo/MMAl exhibited enhanced carbon resistance, in which only 2.3% carbon formed on the catalyst surface, lower than a unimodal mesoporous alumina-supported NiCo catalyst (NiCo/MAl, 12%) and Ni catalyst (Ni/MAl, 24%). The kinetic study suggested that on the unimodal mesoporous alumina, alloying Ni with Co increased the activation energy of CH4 dissociation (∼66 kJ/mol) compared to Ni/MAl (51.7 kJ/mol), thus showing high activity for suppressing CH4 dissociation. In addition, the large-sized mesoporous structure on NiCo/MMAl favored mass transport. As a result, the enhanced carbon resistance for NiCo/MMAl was not only attributed to the suppression of CH4 dissociation by Ni-Co alloy but also to the promotive effect of the large-sized mesopore structure on enhancing mass transport.

Highly efficient solar-driven CO2-to-fuel conversion assisted by CH4 over NiCo-ZIF derived catalysts

Solar-driven CO2 reduction by CH4 is promising to simultaneously tackle energy shortage and global warming problems by converting two greenhouse gases into fuels. However, serious challenges remain, such as limited light-to-fuel efficiency, high operating temperature, and severe catalyst deactivation. Here, high-performance direct solar-driven CO2 reduction is demonstrated at relatively low operation temperature (594 °C) based on NiCo-ZIF derived nanostructures. An ultrahigh light-to-fuel efficiency of 32.4% and production rates of H2 (105.83 min−1g−1) and CO (128.17 mmol min−1g−1) are achieved via photothermocatalysis on Ni1Co2@CZIF-Al2O3 catalysts. Excellent light-to-fuel conversion performance can be attributed to the highly dispersed metal particles, decreased apparent activation energy under direct light illumination, increased CO2 absorption, and promoted dissociation of CH4 to CH3* of NiCo alloy. The carbon deposition rate of NiCo bimetallic catalysts is prominently inhibited compared with pure Ni or Co catalysts due to the change of the reaction path, as confirmed by DFT calculations. This work opens new routes to achieve highly efficient solar-driven CO2 reduction by CH4 based on NiCo-ZIF derived alloy nanostructures at relatively low-temperature conditions.

Density-functional theory investigation into the role of Fe doping for improving the carbon resistance over Ni3Fe(1 1 1) surface in methane reforming with CO2

Density functional theory calculations were performed to provide insights into the effect of iron doping in Ni3Fe(111) catalyst toward the carbon resistance during methane reforming with CO2. The single adsorption (CHx (x = 0–4) and H), co-adsorption between CHx (x = 0–3) and H, the rate constant of each dissociation reaction on Ni3Fe(111) and Ni(111) surfaces were comparatively investigated. The oxygen pre-adsorption calculation was also carried out to find out the reason for the effective carbon resistance on Ni3Fe catalyst. The energy barrier in the rate determining step (CH dissociation) on Ni3Fe (111) surface was lower than that on Ni(111) surface, the former appeared more favorable for carbon formation. However, considering the pre-adsorption of O which was dissociated from CO2, CH species tended to react with pre-adsorbed O to generate CHO, rather than directly dissociate into C. In addition, the relative rate of C binding with O to form CO on Ni3Fe(111) was much faster than that on pure Ni(111) when compared with the rate of CH dehydrogenation. Consequently, the carbon deposition on Ni3Fe catalyst could be effectively suppressed. The catalytic performance of methane reforming with CO2 further experimentally verified that the carbon deposition on Ni3Fe/γ-Al2O3 was less than that on Ni/γ-Al2O3.

Plasma-assisted dry reforming of methane over Mo2C-Ni/Al2O3 catalysts: Effects of β-Mo2C promoter

Non-thermal plasma (NTP) coupled with catalysis provides a way to enable the dry reforming of methane (DRM) reaction to occur at low temperatures. While assistance of NTP brings the negative issue of coke deposition due to the faster rate of CH4 dissociation induced by NTP. Herein, β-Mo2C was employed as an effective component to activate CO2 and collaborated with Ni/γ-Al2O3 for the plasma-assisted DRM reaction. Addition of β-Mo2C facilitated the charge deposition, and Ni nanoparticles were found to re-disperse over the β-Mo2C surface due to the strong interaction between Ni and β-Mo2C. Benefiting from the new active interface of Ni-Mo2C, the mechanically mixed Mo2C-Ni/Al2O3 catalyst exhibited much better activity and stability as compared with the undoped Ni/Al2O3 catalyst. The present study reveals the crucial roles of β-Mo2C additives, providing practical solutions to depress carbon deposition, and thereby enhance the catalytic stability in plasma-assisted DRM reaction.

Discharge dynamics, plasma kinetics and gas flow effect in argon–acetylene discharges

We investigated capacitively coupled Ar/C2H2 RF plasmas with a 1D fluid model that couples a 13.56 MHz discharge module, a long timescale chemical module and a flow transport module. A new solution procedure was developed in order to accurately describe the coupling between the short timescale discharge dynamics and the long characteristic time processes that play a major role in the molecular growth of reactive species. The plasma was simulated for different inlet gas configurations and flowrates. We showed that for a showerhead configuration one may distinguish two situations. For short residence time the plasma was strongly electronegative in the very center of the discharge gap and dominated by large hydrocarbon positive and negative ions. In this situation the acetylene conversion, although moderate, lead to a significant molecular growth. For long residence time, although C2H2 underwent a total conversion, the products of the primary C2H2 dissociation process were consumed by surface deposition which reduced drastically the molecular growth in the short gap discharge considered here. Whatever the conditions, we confirmed the key-role of Ar* in the acetylene conversion, ionization kinetics as well as the subsequent molecular growth for neutral and charged species. We also showed that remote feed gas and showerhead configurations predicted similar results at low flowrate. At larger flowrate the two configurations presented some discrepancy. Especially H2 density was much larger for the remote feed gas configuration, which affected the overall plasma behavior. Our results highlight that realistic gas-flow models are essential for an accurate description of acetylene conversion in Ar/C2H2 plasma.

Looking inside a Ni-Fe/MgAl2O4 catalyst for methane dry reforming via Mössbauer spectroscopy and in situ QXAS

The evolution of the constituents of an 8 wt%Ni-5 wt%Fe/MgAl2O4 catalyst for dry reforming of methane (DRM) is monitored by in situ quick X-ray absorption spectroscopy (QXAS) and 57Fe Mössbauer spectroscopy. In as prepared state, Fe is present as NiFe2O4 at the surface and as MgFe3+xAl2−xO4 within the support, whereas Ni is mainly present as NiO. During H2-TPR, NiFe2O4 and NiO form an alloy from 500 °C on and MgFe3+xAl2−xO4 is partially reduced to MgFe2+xAl2−xO4, such that Ni-Fe alloy, MgFe2+xAl2−xO4 and MgFe3+xAl2−xO4 are the prevalent phases in the reduced catalyst. During DRM, dominantly oxidizing environments (CH4/CO2 = 1/2, 1/1.5) lead to formation of FeOx nanoparticles at the surface of the Ni-Fe alloy, thereby affecting the DRM activity, and possibly to some reincorporation of Fe into the support. For CH4/CO2 = 1/1, no significant changes occur in the catalyst’s activated state, as a consequence of reduction by CH4 dissociation species counteracting oxidation by CO2. However, Mössbauer analysis detects continued extraction of Fe from the support, sustaining ongoing Ni-Fe alloying.

Lanthanide oxide modified nickel supported on mesoporous silica catalysts for dry reforming of methane

Addition of rare earth oxide, especially lanthanide oxide, was regarded as a promising strategy to improve the carbon resistance for Nickel-based catalysts in dry reforming of methane (DRM). In this work, Nickel-based catalysts containing lanthanide oxides (NiLa/SiO2, NiCe/SiO2, NiSm/SiO2, and NiGd/SiO2) were prepared and employed to catalyze DRM. Lanthanide oxide affected the formation of Ni nanoparticles in different size. In NiLa/SiO2 and NiCe/SiO2, Ni nanoparticles maintained relatively small size (4 nm), while in NiSm/SiO2 and NiGd/SiO2, nickel particles were in large size (8 nm). NiLa/SiO2 and NiCe/SiO2 exhibited better stability than the other two catalysts, with CH4 conversion decreasing from 64.6 to 57.6% and 61.6 to 60.3%, respectively in 10 h on stream. The kinetic study confirmed that adding lanthanide oxide significantly affected the activation energy of CH4 dissociation and CO2 dissociation. Compared to monometallic Ni/SiO2, the presence of Sm and Gd suppressed CO2 dissociation, and introduction of Ce and La effectively promoted CO2 dissociation. These characters contributed to the higher carbon resistance and good stability for NiLa/SiO2 and NiCe/SiO2 catalysts in DRM reaction.