N configuration control of N-doped carbon for stabilizing Cu nanoparticles: The synergistic effects on oxy-carbonylation of methanol

Abstract(#br)N-doped carbons (NCs) have attracted considerable attention for their outstanding physicochemical properties, including tunable porosity, electronic features and modified surface. Here, we report the preparation of hierarchically porous NCs derived from the direct pyrolysis of ZIFs (ZIF-7 and ZIF-8) and poly– m –phenylenediamine-covered carbon black (P m PDA-C) for the stabilization of Cu nanoparticles (NPs). The configuration of N species can be effectively regulated by changing the ligand of ZIFs and pyrolysis atmosphere. A remarkable N configuration synergistic effect is observed in the oxy-carbonylation of methanol to dimethyl carbonate with molecular oxygen. The results indicate that the Cu NPs on pristine carbon have a turn over frequency (TOF) of 4.4 h −1 for the reaction, while those on NCs from ZIF-8 and ZIF-7 present TOF values as high as 17.9 h −1 and 28.5 h −1 , respectively. The extensive characterizations reveal that NCs with a nitrogen content of 2–5 wt% and a pyrrolic-/pyridinic-N molar ratio of 2–3 are vital for the performance enhancement of Cu NPs. This work shows that the stabilization and enhanced performance of active Cu NPs on NCs are realized by the rational design of precursors to generate the proper N configurations

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

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

Investigation of cleat and micro-fracture and its aperture distribution in the coals of different ranks in North China: Relative to reservoir permeability

The apertures of cleats and micro-fractures in coal play an important role in the permeability of the coal bed. In this study, optical microscopy and scanning electron microscopy were used to investigate the morphology of cleats and micro-fractures and their apertures, distribution of minerals, and matrix/fracture interactions. The neighboring mineralized and unmineralized cleats suggest the possibility of multi-stage evolutionary processes of cleat formation during the coalification process. The micro-fracture distribution of coals is closely related to their components, including organic macerals and inorganic minerals. Micro-fractures are prone to developing at the junction surface of organic macerals or the surface of organic and inorganic minerals. A mineral-genetic micro-fracture can be classified as an intra-crystal micro-fracture, an extra-crystal micro-scale fracture, or a grain-edge micro-scale fracture. Compared with the low- and middle-ranking coals, cleat and micro-scale fractures in high-ranking coal are usually filled with carbonate minerals and clay minerals. Statistical analysis reveals that the aperture distribution of cleat and micro-fracture in coal shows a log-normal distribution. The aperture of cleat and micro-fracture shows a decreasing trend with increase in coal rank. For low-ranking coal, cleats contribute more to the permeability than micro-fractures. However, for the middle- and high-ranking coals, the contribution of cleats and micro-fractures to the coal reservoir permeability will be close. As the rank of coal increases, the degree of cleat contribution to reservoir permeability decreases, while the degree of micro-fracture contributing to the reservoir permeability increases. Possible reasons for the extremely low reservoir permeability in China may be the following: 1) subsurface cleats and micro-fractures close their apertures significantly due to the in situ geo-stress or 2) cleats and micro-fractures have better permeability in the geological history, which makes the precipitation of minerals decrease the coal reservoir permeability. Therefore, the acid solvent (e.g., HAc, HCl, and HF) added to the drilling or hydraulic fracturing fluid or the geo-stress relief technologies may be an effective way of enlarging the cleat or micro-fracture aperture and enhance the reservoir permeability for coalbed methane production

Product tunable behavior of carbon nanotubes-supported Ni?Fe catalysts for guaiacol hydrodeoxygenation

Bimetallic Ni–Fe nanoparticles supported on carbon nanotubes (CNTs) are prepared and evaluated for the catalytic hydrodeoxygenation (HDO) of a lignin-derived model compound guaiacol. Appropriate combination of Ni and Fe affords high activity and significantly enhances selectivity to cyclohexane or phenol, whereas monometallic Ni and Fe catalysts display poor activities or selectivities. The product tunable behavior of guaiacol HDO is found to be dependent on Ni/Fe atomic ratios. Cyclohexane and phenol are the major products over Ni5–Fe1/CNT with Ni/Fe atomic ratio at 5/1 and Ni1–Fe5/CNT with Ni/Fe atomic ratio at 1/5, respectively. Characterization results confirm that Ni–Fe alloys are formed and elicit synergistic effects on the HDO performance. The selectivity-switchable performance of Ni–Fe/CNT can be assigned to the synergism between Ni domains, where H2 can be easily activated, and Fe domains, which exhibited strong oxophilicity. The bimetallic catalysts give an enhanced stability without significant sintering of metal nanoparticles, while the monometallic catalysts show obvious deactivation due to the agglomeration of metal nanoparticles. Further results reveal that the conversion of guaiacol depends on not only the chemical state but also the size of the metallic nanoparticles. The catalysts with appropriate Ni/Fe atomic ratio and smaller particle perform better hydrogenolysis of C–O bonds, resulting in high selectivity to cyclohexane or phenol

Structural tuning and catalysis of tungsten carbides for the regioselective cleavage of C-O bonds

Tungsten carbides exhibit excellent performance in many heterogeneous processes because of their distinctive catalytic properties. Preparation of tungsten carbides with controllable phase composition relevant to their catalytic behavior is essential yet challenging. In this study, tungsten carbides embedded in carbon spheres (WxC@CS) were fabricated through carburization of organic–inorganic hybrid precursors. W1.25C@CS with rational structure-tuning properties exhibits promising regioselectivity (reaching 91.5%) toward aryl CO bond cleavage, specifically during hydrogenolysis of guaiacol to phenol. A structure reconstruction strategy was adopted to elucidate structure–performance relationship by transforming commercially available bulk WC from inert phase to composition-dependent active catalysts. Combined catalytic and characteristic analyses illustrate that the catalyst performance is dependent on the C-defect structure. The intimate connection between the phenol space time yield and the C/W atomic ratio on the exterior interface of the catalyst was verified. The C/W atomic ratio of 7.2 leads to the optimal catalytic performance. Density functional theory calculations were performed to define the catalytic mechanism at the atomic level. The theoretical analysis suggests an appropriate configuration of surface W and C atoms for activation of hydrogen and guaiacol molecules, rendering the intrinsic active sites for phenol production. This work provides insights into controlling the surface compositions of tungsten carbides to develop efficient CO bond cleavage catalysts, which verifies the importance of hydrogenolysis catalysis in lignin-derived compounds involving complex O-containing guaiacols and phenolics

High circulating CD39+ regulatory T cells predict poor survival for sepsis patients

SummaryBackgroundSepsis encompasses two phases, the ‘hyper’-reactive phase and the ‘hypo’-reactive phase. The initial inflammatory stage is quickly counterbalanced by an anti-inflammatory response, which compromises the immune system, leading to immune suppression. Regulatory T cells (Tregs) have been implicated in the pathogenesis of sepsis by inducing immunosuppression; however, the role of CD39+ Tregs in the process of sepsis is uncertain. This study investigated the dynamic levels of CD39+ Tregs and their phenotypic change in sepsis.MethodsFourteen patients with systemic inflammatory response syndrome (SIRS), 42 patients with sepsis, and 14 healthy controls were enrolled. Sequential blood samples were used to analyze the numbers of CD39+ Tregs and their phenotypic changes. Survival at 28 days was used to evaluate the capacity of CD39+ Treg levels to predict mortality in sepsis patients.ResultsSepsis patients displayed a high percentage (3.13%, 1.46%, and 0.35%, respectively) and mean fluorescence intensity (MFI) (59.65, 29.7, and 24.3, respectively) of CD39+ Tregs compared with SIRS patients and healthy subjects. High-level expression of CD39+ Tregs was correlated with the severity of sepsis, which was reflected by the sepsis-related organ failure assessment score (r=0.322 and r=0.31, respectively). In addition, the expression of CD39+ Tregs was associated with survival of sepsis patients (p<0.01). By receiver-operating characteristic (ROC) curve analysis, the percentage and MFI of CD39+ Tregs showed similar sensitivities and specificities to predict mortality (74.2% and 85.1%, and 73.9% and 84.1%, respectively). Using Kaplan–Meier curves to assess the impact of CD39+ Tregs percentage and MFI on overall survival, we found that a high CD39+ Tregs percentage (p<0.001; >4.1%) and MFI (p<0.001; >49.2) were significantly associated with mortality. Phenotypically, CD39+ Tregs from sepsis patients showed high expression of CD38 and PD-1 (p<0.01 and p<0.01 respectively).ConclusionsIncreased expression of CD39+ Tregs was associated with a poor prognosis for sepsis patients, which suggests that CD39+ Treg levels could be used as a biomarker to predict the outcome of sepsis patients