Comprehensive Analysis of Connectivity and Permeability of a Pore-Fracture Structure in Low Permeability Seam of Huainan-Huaibei Coalfield.

The connectivity and permeability of the coal seam pore structures control the occurrence and migration of coalbed methane. Coal samples were used from Huainan-Huaibei to reconstruct three-dimensional models of the pores and an equivalent pore network model, Statistical pore structure characteristic parameters. The pore structure of the coal reservoir was analyzed from the direction of multidimensional and multiangle. It shows that based on quantitative analysis, the representative Elementary volume of 500 × 500 × 500 was the most suitable experimental volume. The Y-axis direction of the Renlou sample had poor pore connectivity compared to that of other samples. Large volume connected pores dominated their pore systems. In terms of coal sample pore connectivity, the coal samples from the Liuzhuang and Qidong regions had pore connectivity better than those from the other regions. The pore connectivity of the Liuzhuang coal samples was the best. In terms of coal permeability, the Liuzhuang sample had better permeability than the other three samples, and the permeability was the best in the Y-axis direction. For all the combinations of the different types of throats, the shorter the throat, the greater the equivalent radius and the better the permeability. Conversely, the worse the permeability. During gas injection production, the closer the gas injection area was to the gas injection well, the poorer the connectivity and the lower the permeability over time. Near the production area, where the CO2 did not reach the production area, the fracture porosity and effective connected porosity of the coal reservoir increased over time. When CO2 reached the production area, the change in its connected pore structure was consistent with the change in the connected pores in the gas injection area. With this study, the coal seam pore structure on a microscale was characterized. A comprehensive analysis of the coal reservoir pore connectivity and permeability was completed. The study results are significant for the exploration and development of coalbed methane in the Huainan-Huaibei coalfield.

Modeling of Supercritical CO2 Adsorption for Low-Permeability Coal Seam of Huainan-Huaibei Coalfield, China.

Investigating the coal adsorption behavior on supercritical CO2 (ScCO2) is crucial for long-term CO2 geological storage. In this paper, low-permeability coal samples from the Huainan-Huaibei coalfields in China were selected. The high-pressure isothermal adsorption of CO2 was carried out at 36, 42, and 48 °C. The results of adsorption experiments were analyzed by fitting 9 types of modified adsorption models, including three different adsorption theories. Considering that different adsorption mechanisms may exist for CO2 in coal, 14 mixed adsorption models were established. The accuracy of the coefficient of determination (R2) and root-mean-square error (RMSE) for ScCO2 excess adsorption capacity was analyzed, mainly focusing on the accuracy of the key model parameters such as the adsorption phase density and the theoretical adsorption capacity. These parameters were discussed, combined with the predicted adsorption phase density of CO2 based on the intercept method. The results indicate that among the 9 types of modified adsorption considered, based on the adsorption phase density screening, the deviation of the predicted adsorption capacity from the experimental value was then considered. The Dubinin-Radushkevich (DR) model can effectively fit the adsorption behavior of CO2 at low pressure (<7.5 MPa). The Langmuir (L), Langmuir-Freundlich (LF), Extended-Langmuir (EL), and TOTH models can effectively fit the adsorption behavior of CO2 at high pressure (7.5-20 MPa), while the multimolecular layer models were unsuitable for fitting ScCO2 adsorption. The model fitting results showed that only the monomolecular layer and micropore-filled adsorption models were suitable for fitting the ScCO2 adsorption capacity. The DR-LF model best fits the adsorption data based on its key parameters of adsorption phase density and theoretical adsorption capacity. The established mixed model DR-LF fitting results showed that the CO2 in coal was dominated by microporous filling adsorption. The higher the temperature, the greater the contribution of microporous filling adsorption to the total adsorption. There still exists deviation in the adsorption phase density and theoretical adsorption capacity. The contribution percentage of different adsorption mechanisms of CO2 in coal needs to be further investigated.

3D Reconstruction of Pore and Fracture Structures in Crushed Soft Coal with Low Permeability and Its Permeability Analysis: Implications for the Design of CO2 Injection and CH4 Production.

In order to improve the CO2 injection and CH4 production efficiencies during the CO2-ECBM process, it is necessary to clarify the relationship among the complexity of pore and fracture structures, the typicality of the fluid migration path, and the heterogeneity of reservoir permeability. In this study, crushed soft coal with low permeability from Huainan and Huaibei coalfields of China was taken as the research object. First, the three-dimensional (3D) visualization reconstruction of pore and fracture structures was realized. Second, the equivalent pore and fracture network model was constructed. Finally, the permeability evolution and its anisotropy of the coal reservoir were dynamically demonstrated. In this study, the implication of surface porosity on the heterogeneity of pore and fracture structures was first discussed, followed by the implication of coordination number on the anisotropy of fluid flow, and finally, the influence of the anisotropy of fluid flow on the CO2-ECBM process was discussed. The results show that the equivalent pore and fracture network models of the reservoir structure can be constructed based on the digital rock physics technology. The analysis results of porosity, interconnected porosity, typical path of fluid migration, absolute permeability, and surface porosity of each sample have good consistency in characterizing the complexity of pore and fracture structures and the heterogeneity of permeability. The average coordination numbers of RL and LZ samples are 5.99 and 5.78, respectively, and the number of pores and throats is well-balanced, which indicates that LZ and RL collieries are suitable for the development of CO2-ECBM industrial tests. When the interconnected pores and fractures are mainly developed vertically and horizontally, the construction of drilling technology of the CO2-ECBM process should be mainly designed for vertical wells and horizontal wells, respectively. This study has important theoretical and practical significance for the industrial testing and commercialization of CO2-ECBM technology in crushed soft coal with low permeability.

Facile Construction of Nanostructured Cermet Anodes with Strong Metal-Oxide Interaction for Efficient and Durable Solid Oxide Fuel Cells.

Nanostructured anodes generate massive reaction sites to oxidize fuels in solid oxide fuel cells (SOFCs); however, the nonexistence of a practically viable approach for the construction of nanostructures and the retention of these nanostructures under the harsh operating conditions of SOFCs poses a significant challenge. Herein, a simple procedure is reported for the construction of a nanostructured Ni-Gd-doped CeO2 anode based on the direct assembly of pre-formed nanocomposite powder with strong metal-oxide interaction. The directly assembled anode forms heterointerfaces with the electrolyte owing to the electrochemical polarization current and exhibits excellent structural robustness against thermal ripening. An electrolyte-supported cell with the directly assembled anode produces a peak power density of 0.73 W cm-2 at 800 °C, while maintaining stability for 100 h, which is in contrast to the drastic degradation of the cermet anode prepared using the conventional method. These findings provide clarity on the design and construction of durable nanostructured anodes and other electrodes for SOFCs.

Effects of Supercritical CO2 on the Pore Structure Complexity of High-Rank Coal with Water Participation and the Implications for CO2 ECBM.

To reveal how mineral changes affect a coal pore structure in the presence of water, an autoclave was used to carry out the supercritical CO2 (ScCO2)-H2O-coal interaction process. To reveal the changes in pore complexity, mercury intrusion capillary pressure (MICP), low-pressure nitrogen adsorption, CO2 adsorption, and field emission scanning electron microscopy (FESEM) experiments were combined with fractal theory. The experimental data of MICP show that the MICP data are meaningful only for the pore fractal dimension with pore sizes >150 nm. Therefore, the pores were classified into the classes >150, 2-150, and <2 nm. The results show that the pore volume and specific surface area of the coal increased significantly after the reaction. ScCO2-H2O can cause the formation of many new pores and fractures in the coal. The presence of H2O may increase the potential for the injection of CO2 into the coal seam. The complete dissolution of calcite surfaces caused a significant increase in the pore volume and specific surface area of the pores >150 nm. The morphologies of these pores are controlled by the morphologies of the complete dissolution carbonate particles. The pore morphologies were relatively uniform, and the fractal dimensions decreased. However, the incomplete dissolution of calcite leads to irregular variations in the morphologies for the pores in the 2-150 nm pore size range. The pore morphologies that are produced by incompletely dissolved calcite particles are more complex, which increases the fractal dimensions after the reaction. The fractal dimensions of the pores <2 nm decreased after the reaction, indicating that the newly generated micropores were more uniform and had regular pore morphologies.

Correlation Evaluation and Schematic Analysis of Influencing Factors Affecting Pore and Fracture Connectivity on the Microscale and Their Application Discussion in Coal Reservoir Based on X-ray CT Data.

The connectivity of the pore/fracture system is the key to CO2 injection and CH4 production, which is of great significance in analyzing the correlation and weight of the influencing factors affecting the connectivity on the microscale. First, the 3D reconstruction of the coal reservoir is realized. Second, the characteristic parameters of pore/fracture structures are analyzed. Next, the characteristics of absolute permeability are analyzed, and then the correlation and weight analysis of the influencing factors are realized. Finally, the schematic analysis and application discussion of the influencing factors are carried out. The results show that porosity is the key factor restricting fluid migration. The heterogeneity of the reservoir can be characterized by the volume changes of the pore/fracture, organic matter, and mineral. The interconnected pores/fractures are mainly distributed in sheets and bands. The coordination number ranges from 1 to 15. The Ferret diameter is 0-10 µm. The tortuosity is 2.27111, 1.9034, 3.98522, and 3.51516, respectively, and the Euler characteristic number is 0.931868, 0.974719, 0.921144, and 0.897697, respectively. The permeability of the SH and YW samples is higher than that of the RL and PY samples. The single weight of the influencing factor is as follows: coordination number > Ferret diameter > Euler characteristic number > porosity > tortuosity. The analysis area of the comprehensive evaluation score of the influencing factors and the permeability value can be divided into three grades. There is a positive correlation among the coordination number, the quantity equilibrium of pores and throats, and the connectivity. The shape factor gradually increases with the increase of the Ferret diameter. The reservoir permeability is indirectly characterized by the coordination number, Ferret diameter, tortuosity, Euler characteristic number, and shape factor. This study can provide new ideas for clarifying the correlation degree and weight value of the characteristic parameters and can enrich the development of 3D digital core and CO2-ECBM technology.

Dispersed surface Ru ensembles on MgO(111) for catalytic ammonia decomposition.

Ammonia is regarded as an energy vector for hydrogen storage, transport and utilization, which links to usage of renewable energies. However, efficient catalysts for ammonia decomposition and their underlying mechanism yet remain obscure. Here we report that atomically-dispersed Ru atoms on MgO support on its polar (111) facets {denoted as MgO(111)} show the highest rate of ammonia decomposition, as far as we are aware, than all catalysts reported in literature due to the strong metal-support interaction and efficient surface coupling reaction. We have carefully investigated the loading effect of Ru from atomic form to cluster/nanoparticle on MgO(111). Progressive increase of surface Ru concentration, correlated with increase in specific activity per metal site, clearly indicates synergistic metal sites in close proximity, akin to those bimetallic N2 complexes in solution are required for the stepwise dehydrogenation of ammonia to N2/H2, as also supported by DFT modelling. Whereas, beyond surface doping, the specific activity drops substantially upon the formation of Ru cluster/nanoparticle, which challenges the classical view of allegorically higher activity of coordinated Ru atoms in cluster form (B5 sites) than isolated sites.

Ultrafine, Dual-Phase, Cation-Deficient PrBa0.8Ca0.2Co2O5+δ Air Electrode for Efficient Solid Oxide Cells.

Nanostructured air electrodes play a crucial role in improving the electrocatalytic activity of oxygen reduction and evolution reactions in solid oxide cells (SOCs). Herein, we report the fabrication of a nanostructured BaCoO3-decorated cation-deficient PrBa0.8Ca0.2Co2O5+δ (PBCC) air electrode via a combined modification and direct assembly approach. The modification approach endows the dual-phase air electrode with a large surface area and abundant oxygen vacancies. An intimate air electrode-electrolyte interface is in situ constructed with the formation of a catalytically active Co3O4 bridging layer via electrochemical polarization. The corresponding single cell exhibits a peak power density of 2.08 W cm-2, an electrolysis current density of 1.36 A cm-2 at 1.3 V, and a good operating stability at 750 °C for 100 h. This study provides insights into the rational design and facile utilization of an active and stable nanostructured air electrode of SOCs.

Composition, Origin, and Accumulation Model of Coalbed Methane in the Panxie Coal Mining Area, Anhui Province, China.

To investigate the geochemical characteristic, genetic types, and accumulation model of coalbed methane (CBM), 16 samples from a burial depth of 621-1494 m were collected in the Panxie Coal Mining Area of Huainan Coalfield. The results indicate that the samples are dominated by methane, and the concentrations are distributed in the range of 73.11-95.42%. The dryness coefficient is 0.77-1.00 (average, 0.93), and the ratio of methane to the sum of ethane and propane (C1/(C2 + C3)) is 3.18-242.64 (average, 36.15). The δ13CCH4 values are distributed in the range of -65.44 to -32.38‰ (average, -45.22‰), the δDCH4 values are in the range of -226.84 to -156.82‰ (average, -182.93‰), and the δ13CCO2 values are in the range of -19.7 to -10.1‰ (average, -15.51‰). CBM samples in the study area are dominated by thermogenic gases, followed by secondary biogenic gases with CO2 reduction. For the percentages of different genetic gases, the distribution range of thermogenic gas is 70.11-97.86%, whereas that of biogenic gas is 58.65-77.86% for five samples from Zhangji, Panyi, Pansan, and Panbei Coalmines. Moreover, desorption-diffusion fractionation and the effect of groundwater dissolution occurred in the Panxie Coal Mining Area, and higher δ13CCH4 values mostly existed in the deeper coal seams. Furthermore, the biogenic gases are more likely to be secondary biogenic gases generated by CO2 reduction on the basis of data comparison, which is related to the flowing water underground. Accumulation models of different genetic types of CBM are correlated with the burial depth of coal seams, location, and type of faults and aquifers.

Effective Approach with Extra Desorption Time to Estimate the Gas Content of Deep-Buried Coalbed Methane Reservoirs: A Case Study from the Panji Deep Area in Huainan Coalfield, China.

In this study, 11 core coal samples were collected from deep-buried coalbed methane (CBM) reservoirs with burial depth intervals of 900-1500 m for gas estimation content by a direct method. In desorption experiments, the cumulative gas desorption data were recorded within 2 h in the field on the basis of the China National Standard method. For accuracy, two improved methods were proposed. The results show that the gas contents of deep-buried coal samples based on the China National Standard and mud methods are 3.58-9.89 m3/t (average of 6.03 m3/t) and 3.74-10.05 m3/t (average of 6.20 m3/t), respectively. The proposed Langmuir equation and logarithmic equation methods exhibited nonlinear relationships between the cumulative desorption volume and desorption time, which yield values of 6.33-13.34 m3/t (average of 9.36 m3/t) and 6.15-13.86 m3/t (average of 10.37 m3/t), respectively. In addition, the two proposed methods combine the raw data within 2 h by the China National Standard method and additional desorption points during extra time, which are helpful for the ability of the hypothetical methods to calculate the gas content. The Langmuir equation method is a relatively more accurate method to estimate the gas content in comparison with the proposed logarithmic method, which is based on the relative error and comparison plots of actual data and simulated results. From the perspective of numerical value, the Langmuir equation method gives values 1.06-3.39 times (average of 1.86 times) those of the China National Standard method. These analyses show that the proposed Langmuir equation method with extra desorption points is an effective method to determine the gas content of deep-buried CBM reservoirs.

Methodology for Lost Gas Determination from Exploratory Coal Cores and Comparative Evaluation of the Accuracy of the Direct Method.

In the coal exploration of China, the commonly used direct method within 120 min has potential errors in lost gas calculation of deep coal seam for its complex geological conditions. The exploration of deep coal resources by drilling holes in Huainan of Eastern China offered an opportunity to starting research into developing a new method. A developed method with error analysis was constructed to estimate the lost gas using the total desorption process obtained from exploratory coal cores. The accuracy of the direct method was also evaluated comparatively. The result shows that the desorption curve of tested coal samples matches the fitted curve equation. Desorption temperature and the tectonic coal with associated pore characteristics significantly affect the variation of the adsorption characteristics and the estimation of lost gas. The direct method obviously underestimates the lost gas, and methodology using a new lost gas estimation procedure with additional residual gas allows for achieving relatively accurate results of the determination of gas content in coal seams. The calculated result of the new method is about 1.00-1.41 times that of the direct method. The error analysis of desorption results allowed us to determine the dependence between the time (retrieval time and desorption time) and determination method. The time used for desorption in the tank is allowed to extend to less than 400 min or more than 1000 min, which is very potentially important to accurately get the coalbed gas content for coring samples, especially deep exploratory cores for field application.

Direct Visualization of Substitutional Li Doping in Supported Pt Nanoparticles and Their Ultra-selective Catalytic Hydrogenation Performance.

It has only recently been established that doping light elements (lithium, boron, and carbon) into supported transition metals can fill interstitial sites, which can be observed by the expanded unit cell. As an example, interstitial lithium (int Li) can block H filling octahedral interstices of palladium metal lattice, which improves partial hydrogenation of alkynes to alkenes under hydrogen. In contrast, herein, we report int Li is not found in the case of Pt/C. Instead, we observe for the first time a direct 'substitution' of Pt with substitutional lithium (sub Li) in alternating atomic columns using scanning transmission electron microscopy-annular dark field (STEM-ADF). This ordered substitutional doping results in a contraction of the unit cell as shown by high-quality synchrotron X-ray diffraction (SXRD). The electron donation of d-band of Pt without higher orbital hybridizations by sub Li offers an alternative way for ultra-selectivity in catalytic hydrogenation of carbonyl compounds by suppressing the facile CO bond breakage that would form alcohols.

Rapid Interchangeable Hydrogen, Hydride, and Proton Species at the Interface of Transition Metal Atom on Oxide Surface.

Hydrogen spillover is the phenomenon where a hydrogen atom, generated from the dissociative chemisorption of dihydrogen on the surface of a metal species, migrates from the metal to the catalytic support. This phenomenon is regarded as a promising avenue for hydrogen storage, yet the atomic mechanism for how the hydrogen atom can be transferred to the support has remained controversial for decades. As a result, the development of catalytic support for such a purpose is only limited to typical reducible oxide materials. Herein, by using a combination of in situ spectroscopic and imaging technique, we are able to visualize and observe the atomic pathway for which hydrogen travels via a frustrated Lewis pair that has been constructed on a nonreducible metal oxide. The interchangeable status between the hydrogen, proton, and hydride is carefully characterized and demonstrated. It is envisaged that this study has opened up new design criteria for hydrogen storage material.

Preliminary Assessment of the Resource and Exploitation Potential of Lower Permian Marine-Continent Transitional Facies Shale Gas in the Huainan Basin, Eastern China, Based on a Comprehensive Understanding of Geological Conditions.

The Huainan Basin in eastern China contains abundant shale gas resources; the Lower Permian is an exploration horizon with a high potential for shale gas in marine-continent transitional facies. However, few detailed analyses have investigated shale gas in this area. In this paper, a comprehensive investigation of the geochemical characteristics, physical properties, and gas-bearing capacities of shale reservoirs was conducted, and the resource and exploitation potential were evaluated. The results show that the cumulative thicknesses of the Shanxi Formation (P1s) and lower Shihezi Formation (P2xs) are mostly greater than 35 and 65 m, respectively. The TOC contents of the P1s and P2xs shale vary from 0.11 to 8.87% and from 0.22 to 14.63%, respectively; the kerogens predominantly belong to type II with minor amounts of type I or type III kerogens; average R o values range between 0.83 and 0.94% and between 0.82 and 1.02% in P1s and P2xs, respectively; the shale samples are primarily at a low maturity, while some shale samples have entered the high-maturity stage. The shale reservoirs have low permeability and porosity in P1s and P2xs, respectively. The pores of the P1s shale reservoir are characterized by well-developed micropores and transition pores and poorly developed mesopores, while the pores in the P2xs shale reservoir are all characterized by well-developed micropores and transition pores and some well-developed macropores; the different pore types in the shale reservoirs developed in the organic matter, clay minerals, and pyrite, while a few endogenous fractures developed in the organic matter and structural fractures developed in the minerals. The total shale gas contents in P1s and P2xs are 2.85 and 2.96 m3 t-1, respectively. The P2xs shale reservoir has a higher hydrocarbon generation potential than P1s and has a lower gas generation potential. The total shale gas amounts in P1s and P2xs are 3602.29-4083.04 × 108 and 2811.04-3450.77 × 108 m3, respectively. Further research on shale gas exploration and exploitation for these formations needs to be performed.

Stable and Antisintering Tungsten Carbides with Controllable Active Phase for Selective Cleavage of Aryl Ether C-O Bonds.

Transition-metal carbides are important materials in heterogeneous catalysis. It remains challenging yet attractive in nanoscience to construct the active phase of carbide catalysts in a controllable manner and keep a sintering-resistant property in redox reactions, especially hydroprocessing. In this work, an integrated strategy was presented to synthesize stable and well-defined tungsten carbide nanoparticles (NPs) by assembling the metal precursor onto carbon nanotubes (CNTs), wrapping a thin polymeric layer, and following a controlled carburization. The polymer served as a soft carbon source to modulate the metal/carbon ratio in the carbides and introduced amorphous carbons around the carbides to prevent the NPs from sintering. The as-built p-WxC/CNT displayed high stability in the hydrogenolysis of aryl ether C-O bond in guaiacol for more than 150 h. Its activity was more than two and six times higher than those prepared via typical temperature-programmed reduction with gaseous carbon (WxC/CNT-TPR) and carbothermal reduction with intrinsic carbon support (WxC/CNT-CTR), respectively. Our p-WxC/CNT catalyst also achieved high efficiency for selective cleavage of the aryl ether C-O bonds in lignin-derived aromatic ethers, including anisole, dimethoxylphenol, and diphenyl ether, with a robust lifespan.

Spatial Ensembles of Copper-Silica with Carbon Nanotubes as Ultrastable Nanostructured Catalysts for Selective Hydrogenation.

Catalyst deactivation is one of the most important issues in heterogeneous catalysis. Constructing a stable nanoscale structure that maintains efficient activity and prolonged stability under redox conditions for catalysis, particularly hydrogenation reactions, remains attractive albeit the flourishing nanoscience. This work presents a facile route to synthesize a semi-encapsulated transition metal by assembling three-dimensional transition metal silicate nanotubes onto carbon nanotubes (CNTs) as precursors. The obtained materials expose an active surface of the transition metal for efficient catalysis and form a specific structure to inhibit the migration of metal nanoparticles (NPs) by establishing strong metal-support interactions. Cu@SiO2 prepared by common precipitation shows an inferior activity, and its performance is easily attenuated because of the aggregation of Cu NPs. The addition of CNTs as a carrier doubles the intrinsic activity of Cu catalysts. This hybrid catalyst, which consists of Cu species, SiO2, and CNTs, is among the best catalysts for dimethyl oxalate hydrogenation with boosting activity of 25 h-1 and enhanced stability of more than 200 h.

Photodeposition of Pd onto TiO2 nanowires for aqueous-phase selective hydrogenation of phenolics to cyclohexanones.

The selective hydrogenation of phenolics to cyclohexanones is an important process in both industrial application and utilization of fossil and renewable feedstocks. However this process remains a challenge in achieving high conversion of phenolics and high selectivity of ketones under mild reaction conditions. In this work, TiO2 nanowires (TNWs) are successfully synthesized by using an integrated method and the ultra-small Pd clusters were then deposited onto the TNWs by photoreduction. The obtained Pd/TNW catalyst shows superior catalytic performances in the hydrogenation of phenolic derivatives to the corresponding cyclohexanones. In particular, a nearly full conversion of phenol with high selectivity (>99.0%) to cyclohexanone can be achieved at 50 °C and 5.0 bar H2 in water. A series of characterization studies by means of XRD, XPS, EPR, FTIR, TPD, STEM, and kinetic studies indicate that abundant exposed Lewis acid and basic sites on the surface of TNWs play important roles in the activation of phenolics and desorption of cyclohexanones, while the Pd clusters by photodeposition can attain a hybrid of Pd0 and Pd2+ species to facilitate the activation of dihydrogenation. A plausible catalytic pathway with synergistic effects of TNWs and Pd species is then proposed.

Tandem Hydrogenolysis-Hydrogenation of Lignin-Derived Oxygenates over Integrated Dual Catalysts with Optimized Interoperations.

The efficient hydrodeoxygenation (HDO) of lignin-derived oxygenates is essential but challenging owing to the inherent complexity of feedstock and the lack of effective catalytic approaches. A catalytic strategy has been developed that separates C-O hydrogenolysis and aromatic hydrogenation on different active catalysts with interoperation that can achieve high oxygen removal in lignin-derived oxygenates. The flexible use of tungsten carbide for C-O bond cleavage and a nickel catalyst with controlled particle size for arene hydrogenation enables the tunable production of cyclohexane and cyclohexanol with almost full conversion of guaiacol. Such integration of dual catalysts in close proximity enables superior HDO of bio-oils into liquid alkanes with high mass and carbon yields of 27.9 and 45.0 wt %, respectively. This finding provides a new effective strategy for practical applications.

Sulfur Moiety as a Double-Edged Sword for Realizing Ultrafine Supported Metal Nanoclusters with a Cationic Nature.

Heterogeneously and uniformly dispersed metal nanoclusters with high thermal stability and stable nonmetallic nature show outstanding catalytic performance. In this work, we report on the role of sulfur moieties in hydrochlorination catalysis over carbon-supported gold (Au/C). A combination of experimental and theoretical analyses shows that the -SO3H and derived -SO2H sulfur species in high oxidation states at the interface between Au and -SO3H at ≥180 °C give rise to high thermal stability and catalytic activity. By contrast, the grafted thiol group (-SH) and the derived low-valence sulfur species on carbon markedly destabilize the Au nanoclusters, promoting their rapid sintering into large Au nanoparticles and leading to the loss of their cationic nature. Theoretical calculations suggest that -SO3H favorably adsorbs and stabilizes cationic Au species. Compared to Au/C and Au-SH/C with the Auα+/Au0 atomic ratios of 1.02 and 0.24, respectively (α = 1 or 3), the activity and durability of acetylene hydrochlorination are remarkably enhanced by the interaction between the -SO3H moieties and cationic Au species that enables the high oxidation state of Au to be effectively retained (Auα+/Au0 = 3.82). These results clearly demonstrate the double-edged sword effect of sulfur moieties on the catalytic Au component in acetylene hydrochlorination. The double-edged sword effect of sulfur species in the stabilization/destabilization of metal nanoclusters is also applicable to other metals such as Ru, Pd, Pt, and Cu. Overall, this study enriches the general understanding of the stabilization of metal clusters and provides insight into a wet chemistry strategy for stabilizing supported ligand-free nanoclusters.

Intercalation of nanostructured CeO2 in MgAl2O4 spinel illustrates the critical interaction between metal oxides and oxides.

Heterogeneous catalytic oxidation arises from the prerequisite oxygen activation and transfer ability of metal oxide catalysts. Thus, engineering intercalated nanounits and heterophase metal oxide structures, and forming interstitial catalyst supports at the nanoscale level can drastically alter the catalytic performances of metal oxides. This is particularly important for ceria-based nanomaterial catalysts, where the interactions of reducible ceria (CeO2) and nonreducible oxides are fundamental for the preparation of enhanced catalysts for oxygen-involved reactions. Herein, we intercalated nanostructured CeO2 in the bulk phase of magnesium aluminate spinel (MgAl2O4, referred to as MgAl), produced the interstitial effect between CeO2 nanoparticles and MgAl crystallites, thus boosting their oxygen transfer and activation capability. This nanoscaled intercalation engineering significantly enhanced the number and quality of tight contact points between the nanostructured CeO2 and MgAl units. Therefore, the oxygen storage/release capability (OSC) is exceptionally improved as revealed by various characterizations and catalytic carbon oxidation reaction. A mechanism similar to the Mars-van Krevelen process at the nanoscale level was invoked to explain the catalytic oxidation mechanisms. The reactive oxygen species of gaseous O2 originate formed the bulk of the as-obtained nanomaterial, where strong interactions between the CeO2 and MgAl components occured, which were subsequently released and diffused to the catalyst-interface at elevated temperatures. Silver supported on Ce-MgAl produced an approximately 4-fold higher concentration of active oxygen species than Ag/MgAl, and gives the optimum low-temperature oxidation at 229 °C. This study verifies the importance of the redox performance of ceria-spinel with enhanced OSC, which validates that the arrangement of contacts at the nanoscale can substantially boost the catalytic reactivity without varying the microscale structure and properties of spinel.