查看更多>>摘要：Chemical looping concept paves way toward intrinsically safe and efficient oxidative coupling of methane (CL-OCM) process, because it permits the reaction to proceed via repeating reduction-oxidation cycle in two reactors. It is calling for a ground-breaking catalyst with enough high selective CH4-converting lattice-oxygen carrying capacity but represents a grand challenge. Herein, we report an efficient catalyst obtainable by decorating an oxygen carrier FeMnO3 with Na2WO4, with good cycling performance, achieving a high space time yield of 29.8 g(C2-C3) kg(cat)(-1) h(-1) with 20% CH4 conversion and 80% C-2-C-3 selectivity at 800 degrees C and a low catalyst/CH4 weight ratio of 13.5. CL-OCM process is established by "FeMnO3. [MnFe2O4 + MnO]" redox cycle. Na2WO4-decoration gets lattice oxygen stored in FeMnO3 transformed from non-selective to selective due to mitigation of latticeoxygen evolution. Scaled up CL-OCM testing with 10-gram catalyst also yields comparable results seen in the case of using 1-gram catalyst, validating great application potential.
查看更多>>摘要：Ru-based catalysts with increased attention for CVOC purification still have huge challenges in promoting their low-temperature activity and durability. Here, a Cr-modified RuO2/TiO2 catalyst was fabricated and employed for 1,2-dichloroethane (1,2-DCE) destruction. The synergy of Cr2O3 and RuO2/TiO2 enhances the exposure of surface Ru, generating abundant reducible Cr6+ and Ru4+ species and chemically adsorbed oxygen, which promote the activity and CO2/HCl selectivity in 1,2-DCE decomposition evidently. 1,2-DCE primarily activates on the Lewis acid sites (LAS) over RuO2/Cr2O3 /TiO2 with C-Cl cleavage. Meanwhile, C-C cleavage occurs along with the dehydrochlorination and chlorination reactions. The presence of Cr2O3 greatly improves the LAS concentration and redox ability of RuO2/TiO2, accelerating the deep destruction of 1,2-DCE and inhibiting the formation of CH2Cl2, C2HCl3 and CHCl3. Cr species with superior chlorine resistance elevate the durability of RuO2/Cr2O3 /TiO2 under simulated conditions toward H2O, SO2, and chlorine species, making it a promising candidate for industrial CVOC catalytic degradation.
查看更多>>摘要：The development of efficient CO2 conversion catalysts is a long-lasting desire. Herein, we introduce an atomic Pd-promoted ZnZrOx solid solution catalyst (Pd-ZnZrOx), which shows markedly enhanced rate of methanol production compared to bare ZnZrOx, as well as excellent stability over 100 h on stream. Up to 0.8 at% (i.e. 0.6 wt%), Pd can be atomically dispersed in ZnZrOx, leading to more oxygen vacancies on the mixed oxide that foster methanol production. Kinetic analysis and in situ DRIFTS reveal that hydrogen activation is limited on ZnZrOx, but Pd doping facilitates H-2 dissociation as well as the consequent formation of HCOO*, thus boosting CO2 conversion to methanol. DFT analyses suggest that the presence of atomic Pd enables a more exothermic H2 dissociation, which increases the availability of surface H and facilitates CO2 hydrogenation on adjacent Zn sites, providing rationale on the high activity and robustness of Pd-ZnZrOx in CO2 hydrogenation.
查看更多>>摘要：Zeolites with incorporated Zn species are gaining relevance for catalyzing the dehydrogenation of short-chain alkanes. However, the presence of zinc also leads to the C-C cleavage in the alkane, lowering the selectivity to the olefin. We disclose herein the importance of controlling the zeolite particle size and the promoting role of K2O addition to improve the alkene selectivity and catalyst stability during Zn-catalyzed CO2-assisted oxidative dehydrogenation of ethane. In particular, the nano-sized SSZ-13 catalysts outperform the micro-sized SSZ-13 catalysts in terms of C2H6 conversion due to the critical role of zeolite crystal surface properties that improves the dispersion of the Zn phase. The modification of Zn with K2O neutralizes the acidity of the catalysts, suppressing the formation of undesired paths and leading to higher C2H4 selectivity and improved stability. Detailed characterizations and density functional theory show that K2O-neighbored (Zn-O-Zn)(2+) lowers the activation barrier for the surface removal of H-based adsorbates. Overall, these findings demonstrate the roles of fine-tuning acid base properties on the zeolite surface to control the catalytic performance during the CO2-assisted conversion of light alkanes.
查看更多>>摘要：Herein, we report an oxygen vacancy (OVs)-rich Nb2O5 semiconductor (OVs-N-Nb2O5) as a bifunctional heterogeneous photocatalyst for unprecedent synthesis of a-sulfonyloxy ketones via oxidative alkene difunctionalization with sodium sulfinate under visible light irradiation and ambient conditions. A broad set of aromatic and aliphatic alkenes was efficiently difunctionalized into diverse a-sulfonyloxy ketones in high yields with a good functional group tolerance. The catalyst OVs-N-Nb2O5 is highly stable and could be easily recovered for at least 6 successive recycles with maintaining photoactivity and selectivity. Experimental and theoretical investigations reveal that the presence of OVs not only accelerates the separation and transfer of photogenerated electron-hole pairs, but also promotes O-2 adsorption and activation to form long-lived superoxide anion radical (O-2 center dot), which greatly boosts the reaction and modulates the reaction pathways together with the intrinsic Lewis acid sites, thereby resulting in an improved reaction activity and excellent selectivity to the desired product.
查看更多>>摘要：Electrochemical CO2 conversion into fuels is highly desirable to achieve carbon artificial cycles. Among electrocatalyst candidates, earth-abundant tin is subject to unsatisfied efficiency and selectivity. In this work, atomically-dispersed Sn nanoclusters modified with the trace of sulfur doping are proposed to efficiently electroreduce CO2 to C1 chemicals. This electrocatalyst is in situ derived from bis(benzene-1,2-dithiolato). It exhibits a high Faradaic efficiency (90%) for carbonaceous products at a moderate overpotential (0.75 V). Importantly, it is exploited for the formate formation with unprecedented partial current density (90 mA cm-2) and long-term stability (50 h) using the flow cell, better than most Sn-based catalysts. Electrochemical experiments and theoretical calculations manifest the promoting effect of trace sulfur on Sn nanoclusters, which stabilizes the *HCOOH intermediate and favors CO2 electroreduction. Hence, it emphasizes the importance of dopants and charge modulating for performance enhancement. This work unfolds a promising candidate for Sn electrocatalysts towards CO2 electroreduction.
查看更多>>摘要：The simultaneous integration of electronic regulation and architectural engineering in one electrocatalyst represents a powerful leverage to concurrently boost the electrocatalytic performance towards overall water splitting. We herein rationally fabricate Sn4P(3)/Co2P "stalk "- "cap "-typed nanoarrays (Sn4P(3)/Co2P SCNAs) with abundant heterointerfaces and elaborately implanted "caps ". The nanoarrayed structure can substantially enlarge the exposure of active sites and promote the mass/electron transport, thus accelerating the reaction kinetics. Moreover, the purposely grafted "caps " are beneficial to increase the hydrophilicity/aerophobicity, which facilitate the water affinity and release of generated gas bubbles. Accordingly, the obtained Sn4P3/Co2P SCNAs deliver exceptional electrocatalytic performances towards the HER and OER, as reflected by the over potentials of 45.4 and 280.4 mV at 10 mA cm(-2), respectively. More impressively, the two-electrode electrolyzer assembled by freestanding Sn4P(3)/Co2P SCNAs requires a cell voltage of 1.56 V at 10 mA cm(-2) and exhibits superior stability and full reversibility, holding great potential in practical water electrolysis.
查看更多>>摘要：Development of high-performance and stable electrocatalysts for hydrogen evolution reaction (HER) is crucial for hydrogen economy. Inspired by hydrogen evolution behavior on hydrogenase enzyme, in which the azadithiolate bridging ligand of active center facilitates fast proton shuttling and catalytic turnover, here we present an efficient approach to enhance both HER kinetics and stability realizing on an IrNi@N,O-C catalyst with individual IrNi nanoparticle separately confined in N and O co-doped carbon (N,O-C) nanocage. Experimental and theoretical investigations indicate that the N,O-C nanocage provides proton-adsorbing functionality on raising H* coverage over IrNi active centers, resulting in much accelerated HER kinetics. The IrNi@N,O-C presents superior HER performances compared to all reported Ir-based catalysts, with overpotential of 22 mV at 100 mA cm(-2,) ultrahigh mass activity of 9.82 A mg(Ir)(-1) (-0.050 V vs. RHE) and outstanding durability of 200 h at large current density. This work affords fresh insights/strategies for design of high-performance electrocatalysts
查看更多>>摘要：Electrochemical reduction of CO2 to valuable products on molecular catalysts draws attention due to their versatile structures allowing tuning of activity and selectivity. Here, we investigate temperature influence on CO2 conversion product selectivity over a Cobalt(II)-tetraphenyl porphyrin (CoTPP)/multiwalled carbon nanotube (MWCNT) composite in the range of 20-50 degrees C. Faradaic efficiency of products changes with temperature and potential so that two-electron transfer product CO formation is enhanced at low potentials and temperatures while the competing hydrogen formation shows an opposite trend. Multi-electron transfer product methanol formation is more favorable at low temperatures and potentials whereas reverse applies for methane. Activity and selectivity are analyzed with DFT simulations identifying the key differences between the binding energies of CH2O and CHOH, the binding strength of CO, and the protonation of CHO intermediate. This novel experimental and theoretical understanding for CO2 reduction provides insight in the influence of the various conditions on the product distribution.
查看更多>>摘要：The electrochemical reduction reaction of carbon dioxide (CO2RR) is an effective way towards carbon neutralization. Single-atom catalysts (SACs) are expected to be efficient for CO2RR due to maximum atom utilization and excellent catalytic performance. Here, nitrogen-doped carbon supported Ni SACs (Ni-SAC@NCs) were prepared through effective fast pyrolysis. CO2 can convert into CO efficiently with Ni-SAC@NCs as electrocatalysts for CO2RR. The faradaic efficiency kept well above 80% in the applied potential window of -0.6 to -0.9 V (vs. reversible hydrogen electrode (RHE)), with a highest FECO of 95% at -0.6 V (vs. RHE). Ni-SAC@NCs can achieve the best CO selectivity under a small overpotential, surpassing most other state-of-the-art catalysts. Computations also indicate that the unique defect-Ni-N-3 structure is the active site. This work not only provides a simple and promising new route for the preparation of SACs, but also proves the key role of the coordination environment in electrocatalysis.
NSTL
Elsevier