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Lower olefins are widely used in the chemical industry as basic carbon-based feedstocks. Here, we report the catalytic system featuring isolated single-atom sites of iridium (Ir 1 ) that can function within the entire temperature range of 300-600 °C and transform alkanes with conversions close to thermodynamics-dictated levels. The high turnover frequency values of the Ir 1 system are comparable to those of homogeneous catalytic reactions. Experimental data and theoretical calculations both indicate that Ir 1 is the primary catalytic site, while the coordinating C and N atoms help to enhance the activity and stability, respectively; all three kinds of elements cooperatively contribute to the high performance of this novel active site. We have further immobilized this catalyst on particulate Al 2 O 3 , and we found that the resulting composite system under mimicked industrial conditions could still give high catalytic performances; in addition, we have also developed and established a new scheme of periodical in situ regeneration specifically for this composite particulate catalyst.

Cu is a promising electrocatalyst in CO 2 reduction reaction (CO 2 RR) to high-value C 2+ products. However, as important C-C coupling active sites, the Cu + species is usually unstable under reduction conditions. How atomic dopants affect the performance of Cu-based catalysts is interesting to be studied. Herein, we first calculated the difference between the thermodynamic limiting potentials of CO 2 RR and the hydrogen evolution reaction, as well as the *CO binding energy over Cu 2 O doped with different metals, and the results indicated that doping atomic Gd into Cu 2 O could improve the performance of the catalyst effectively. On the basis of the theoretical study, we designed Gd 1 /CuO x catalysts. The distinctive electronic structure and large ion radii of Gd not only keep the Cu + species stable during the reaction but also induce tensile strain in Gd 1 /CuO x , resulting in excellent performance of the catalysts for electroreduction of CO 2 to C 2+ products. The Faradic efficiency of C 2+ products could reach 81.4% with a C 2+ product partial current density of 444.3 mA cm -2 at -0.8 V vs a reversible hydrogen electrode. Detailed experimental and theoretical studies revealed that Gd doping enhanced CO 2 activation on the catalyst, stabilized the key intermediate O*CCO, and reduced the energy barrier of the C-C coupling reaction.

Cu single-atom catalysts (Cu SACs) have been considered as promising catalysts for efficient electrocatalytic CO 2 reduction reactions (ECRRs). However, the reports on Cu SACs with an asymmetric atomic interface to obtain CO are few. Herein, we rationally designed two Cu SACs with different asymmetric atomic interfaces to explore their catalytic performance. The catalyst of CuN 3 O/C delivers high ECRR selectivity with an FE CO value of above 90% in a wide potential window from -0.5 to -0.9 V vs RHE (in particular, 96% at -0.8 V), while CuCO 3 /C delivers poor selectivity for CO production with a maximum FE CO value of only 20.0% at -0.5 V vs RHE. Besides, CuN 3 O/C exhibited a large turnover frequency (TOF) up to 2782.6 h -1 at -0.9 V vs RHE, which is much better than the maximum 4.8 h -1 of CuCO 3 /C. Density functional theory (DFT) results demonstrate that the CuN 3 O site needs a lower Gibbs free energy than CuCO 3 in the rate-determining step of CO desorption, leading to the outstanding performance of CuN 3 O/C on the process of ECRR-to-CO. This work provides an efficient strategy to improve the selectivity and activity of the ECRR via regulating asymmetric atomic interfaces of SACs by adjusting the coordination atoms.

The properties of supports have a significant effect on the activity of noble metal single atoms. In this work, Co-doped CeO 2 -supported single-atom Pt catalysts (Pt 1 /Co-CeO 2 ) have been acquired by a synchronous pyrolysis/deposition route and demonstrated to promote low-temperature oxidation of CO. Revealed by a model reaction of 1% CO + 1% O 2 + 98% He at a space velocity of 12,000 mL/g cat /h, CO conversion (100 °C) acquired on a (0.5% Pt)/(10% Co-CeO 2 ) catalyst (36.6%) was 3.6 and 4.9 times those of 0.5% Pt/CeO 2 (10.0%) and 10% Co-CeO 2 (7.4%) catalysts and 2.1 times that of their conversion sum (17.4%), confirming the positive role of the Co dopant in boosting the low-temperature oxidation of CO. The consistent results are also verified in the comparison of Pt 1 /Co-ZnO with Pt 1 /ZnO and Pt 1 /Co-Al 2 O 3 with Pt 1 /Al 2 O 3 . In addition, the activity of single-atom Pt 1 /Co-CeO 2 catalysts can be facilely modified by changing the loading of Pt and/or doping amount of Co. These reasonable data will provide a methodology to access more applicable catalysts for CO oxidation at low temperature.

Hydrogen production by water splitting and seawater electrolysis is a promising alternative to develop clean hydrogen energy. The construction of high-efficiency and durable electrocatalysts for the hydrogen evolution reaction (HER) in a wide pH range and seawater is critical to overcoming the sluggish kinetic process. Herein, we develop an efficient catalytic material composed of a single-atom Ru-N 4 site and Ru nanoparticles anchored on nitrogen-doped carbon (Ru 1+NPs /N-C) through the coordination-pyrolysis strategy of the melamine formaldehyde resin. The Ru 1+NPs /N-C catalyst shows outstanding HER activity with the smallest overpotentials, the lowest Tafel slopes, the highest mass activity and turnover frequency, as well as excellent stability in both acidic and alkaline media. Moreover, Ru 1+NPs /N-C shows comparable hydrogen production performance and a higher faradic efficiency to 20% Pt/C in natural seawater and artificial simulated seawater. Theoretical calculations demonstrate that the strong synergistic effects between the Ru-N 4 site and Ru nanoparticles modify the electronic structure to accelerate the HER kinetics. Ru nanoparticles can effectively realize dissociation of H 2 O to generate adsorbed hydrogen and also promote the single-atom Ru-N 4 site to combine adsorbed hydrogen to H 2 and desorption. This work provides a new perspective for designing high-efficiency hydrogen production electrocatalysts for large-scale seawater electrolysis.

Photocatalytic CO 2 conversion into a high-value-added C 2 product is a highly challenging task because of insufficient electron deliverability and sluggish C-C coupling kinetics. Engineering catalytic interfaces in photocatalysts provides a promising approach to manipulate photoinduced charge carriers and create multiple catalytic sites for boosting the generation of C 2 product from CO 2 reduction. Herein, a Cu δ+ /CeO 2 -TiO 2 photocatalyst that contains atomically dispersed Cu δ+ sites anchored on the CeO 2 -TiO 2 heterostructures consisting of highly dispersed CeO 2 nanoparticles on porous TiO 2 is designedly constructed by the pyrolytic transformation of a Cu 2+ -Ce 3+ /MIL-125-NH 2 precursor. In the designed photocatalyst, TiO 2 acts as a light-harvesting material for generating electron-hole pairs that are efficiently separated by CeO 2 -TiO 2 interfaces, and the Cu-Ce dual active sites synergistically facilitate the generation and dimerization of *CO intermediates, thus lowering the energy barrier of C-C coupling. As a consequence, the Cu δ+ /CeO 2 -TiO 2 photocatalyst exhibits a production rate of 4.51 μmol -1 ·g cat -1 ·h -1 and 73.9% selectivity in terms of electron utilization for CO 2 to C 2 H 4 conversion under simulated sunlight, with H 2 O as hydrogen source and hole scavenger. The photocatalytic mechanism is revealed by operando spectroscopic methods as well as theoretical calculations. This study displays the rational construction of heterogeneous photocatalysts for boosting CO 2 conversion and emphasizes the synergistic effect of multiple active sites in enhancing the selectivity of C 2 product.

Reducing CO 2 into fuels via photochemical reactions relies on highly efficient photocatalytic systems. Herein, we report a new and efficient photocatalytic system for CO 2 reduction. Driven by electrostatic attraction, an anionic metal-organic framework Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) as host and a cationic photosensitizer [Ru(phen) 3 ] 2+ (phen = 1,10-phenanthroline) as guest were self-assembled into a photocatalytic system Ru@Cu-HHTP , which showed high activity for photocatalytic CO 2 reduction under laboratory light source (CO production rate of 130(5) mmol g -1 h -1 , selectivity of 92.9%) or natural sunlight (CO production rate of 69.5 mmol g -1 h -1 , selectivity of 91.3%), representing the remarkable photocatalytic CO 2 reduction performance. More importantly, the photosensitizer [Ru(phen) 3 ] 2+ in Ru@Cu-HHTP is only about 1/500 in quantity reported in the literature. Theoretical calculations and control experiments suggested that the assembly of the catalysts and photosensitizers via electrostatic attraction interactions can provide a better charge transfer efficiency, resulting in high performance for photocatalytic CO 2 reduction.

Electrochemical reduction of CO 2 to chemicals and fuels is an interesting and attractive way to mitigate greenhouse gas emissions and energy shortages. In this work, we report the use of atomic In catalysts for CO 2 electroreduction to CO. The atomic In catalysts were anchored on N-doped carbon (In A /NC) through pyrolysis of In-based metal-organic frameworks (MOFs) and dicyandiamide. It was discovered that In A /NC had outstanding performance for selective CO production in the mixed electrolyte of ionic liquid/MeCN. It is different from those common In-based materials, in which formate/formic acid is formed as the main product. The faradaic efficiency (FE) of CO and total current density were 97.2% and 39.4 mA cm -2 , respectively, with a turnover frequency (TOF) of ∼40 000 h -1 . It is one of the highest TOF for CO production to date for all of the catalysts reported. In addition, the catalyst had remarkable stability. Detailed study indicated that In A /NC had higher double-layer capacitance, larger CO 2 adsorption capacity, and lower interfacial charge transfer resistance, leading to high activity for CO 2 reduction. Control experiments and theoretical calculations showed that the In-N site of In A /NC is not only beneficial for dissociation of COOH* to form CO but also hinders formate formation, leading to high selectivity toward CO instead of formate.

In the area of catalysis, selective reduction of nitro compounds to amino compounds is a colossal challenge due to the existence of competitive reducible functional groups. Herein, an Fe-based catalyst Fe SAs /Fe 2 O 3ACs /N-doped polyhedral carbon (NPC) has been designed and synthesized. As we expected, compared with Fe SAs and Fe NPs , Fe SAs /Fe 2 O 3ACs /NPC shows excellent catalytic performance (turnover frequency up to 1923 h -1 , calculated with nitrobenzene), chemoselectivity, and tolerance during the hydrogenation reaction of nitro compounds under room temperature because of the synergistic effects between Fe SAs and Fe 2 O 3ACs . The theoretical calculations show that Fe SAs prefers to undergo hydrazine decomposition to generate hydrogen and the Fe 2 O 3ACs surface is more active toward the nitrobenzene reduction to aniline.

Stabilized Cu + species have been widely considered as catalytic active sites in composite copper catalysts for catalytic reactions with industrial importance. However, few examples comprehensively explicated the origin of stabilized Cu + in a low-cost and widely investigated CuO/TiO 2 system. In this study, mass producible CuO/TiO 2 catalysts with interface-stabilized Cu + were prepared, which showed excellent low-temperature CO oxidation activity. A thorough characterization and theoretical calculations proved that the strong charge-transfer effect and Ti-O-Cu hybridization in Ti-doped CuO(111) at the CuO/TiO 2 interface contributed to the formation and stabilization of Cu + species. The CO molecule adsorbed on Cu + and reacted directly with Ti doping-promoted active lattice oxygen via a Mars-van Krevelen mechanism, leading to the enhanced low-temperature activity.

Herein, a series of Fe-based catalysts have been designed and prepared by grinding a mixture of MIL-88d and melamine, and then the mixture was followed by pyrolysis. An unusual Fe/Fe 3 C-activated site is uniformly encapsulated in the N-doped carbon tubes obtained by pyrolysis of the film-like nanocrystals of MIL-88d. Experimental characterizations and theoretical calculations demonstrate that the surface N sites can effectively trap the nitrobenzene and aniline by their phenyl groups with the formation of three C-N bonds that made the catalyst exhibit excellent catalytic activity (turnover frequencies of ≤11268 h -1 calculated on the basis of nitrobenzene) and chemoselectivity for the reduction of nitro derivatives under facile conditions.

A central topic in single-atom catalysis is building strong interactions between single atoms and the support for stabilization. Herein we report the preparation of stabilized single-atom catalysts via a simultaneous self-reduction stabilization process at room temperature using ultrathin two-dimensional Ti 3- x C 2 T y MXene nanosheets characterized by abundant Ti-deficit vacancy defects and a high reducing capability. The single atoms therein form strong metal-carbon bonds with the Ti 3- x C 2 T y support and are therefore stabilized onto the sites previously occupied by Ti. Pt-based single-atom catalyst (SAC) Pt 1 /Ti 3- x C 2 T y offers a green route to utilizing greenhouse gas CO 2 , via the formylation of amines, as a C 1 source in organic synthesis. DFT calculations reveal that, compared to Pt nanoparticles, the single Pt atoms on Ti 3- x C 2 T y support feature partial positive charges and atomic dispersion, which helps to significantly decrease the adsorption energy and activation energy of silane, CO 2 , and aniline, thereby boosting catalytic performance. We believe that these results would open up new opportunities for the fabrication of SACs and the applications of MXenes in organic synthesis.

It is very important to explore novel synthesis strategies for constructing highly active and inexpensive electrocatalysts for water-splitting. In present work, a novel and efficient coordination-polymerization-pyrolysis (CPP) strategy was developed to prepare cobalt phosphide nanoparticles modified N-doped porous carbon spheres (CoP@NPCSs) hybrids as a powerful catalyst for overall water-splitting (OWS). It can be found that both the carbonization temperatures and the metal contents affect the electrocatalytic performances. As a result, a device assembled with CoP@NPCSs demonstrates low potential (1.643 V @ 10 mA·cm -2 ) and good stabilization for OWS. Besides, other transition metal phosphides (TMPs)-based materials also can be synthesized by the CPP approach, evidencing the generality of the CPP strategy. Here, we not only constructs a high-efficiency OWS catalyst, but also broadens the synthetic methodology of TMPs from nanoscale.

Metal-organic frameworks (MOF) have recently emerged as versatile precursors to fabricate functional MOF derivatives for oxygen evolution reactions (OER). Herein, we developed a controlled partial pyrolysis strategy to construct robust NiCo/Fe 3 O 4 heteroparticles within MOF-74 for efficient OER using trimetallic NiCoFe-MOF-74 as precursor. The partial pyrolysis method preserves the framework structure of MOF for effective substrates diffusion while producing highly active nanoparticles. The as-prepared NiCo/Fe 3 O 4 /MOF-74 delivered remarkably stable OER current with an overpotential as low as 238 mV at 10.0 mA cm -2 and an Tafel slop of 29 mV/dec, outperforming those of pristine NiCoFe-MOF-74, totally decomposed MOF derivatives, and most reported non-noble metal based electrocatalysts. The key for the formation of NiCo/Fe 3 O 4 /MOF-74 nanostructures is that the metals can be decomposed from NiCoFe-MOF-74 in the order of Ni, Co, and Fe under controlled heat treatment. Density functional theory calculations reveals that the underlying NiCo promotes the OER activity of Fe 3 O 4 through exchange stabilization of active oxygen species.

We develop an N-coordination strategy to design a robust CO 2 reduction reaction (CO 2 RR) electrocatalyst with atomically dispersed Co-N 5 site anchored on polymer-derived hollow N-doped porous carbon spheres. Our catalyst exhibits high selectivity for CO 2 RR with CO Faradaic efficiency (FE CO ) above 90% over a wide potential range from -0.57 to -0.88 V (the FE CO exceeded 99% at -0.73 and -0.79 V). The CO current density and FE CO remained nearly unchanged after electrolyzing 10 h, revealing remarkable stability. Experiments and density functional theory calculations demonstrate single-atom Co-N 5 site is the dominating active center simultaneously for CO 2 activation, the rapid formation of key intermediate COOH* as well as the desorption of CO.

The construction of highly active and stable non-noble-metal electrocatalysts for hydrogen and oxygen evolution reactions is a major challenge for overall water splitting. Herein, we report a novel hybrid nanostructure with CoP nanoparticles (NPs) embedded in a N-doped carbon nanotube hollow polyhedron (NCNHP) through a pyrolysis-oxidation-phosphidation strategy derived from core-shell ZIF-8@ZIF-67. Benefiting from the synergistic effects between highly active CoP NPs and NCNHP, the CoP/NCNHP hybrid exhibited outstanding bifunctional electrocatalytic performances. When the CoP/NCNHP was employed as both the anode and cathode for overall water splitting, a potential as low as 1.64 V was needed to achieve the current density of 10 mA·cm -2 , and it still exhibited superior activity after continuously working for 36 h with nearly negligible decay in potential. Density functional theory calculations indicated that the electron transfer from NCNHP to CoP could increase the electronic states of the Co d-orbital around the Fermi level, which could increase the binding strength with H and therefore improve the electrocatalytic performance. The strong stability is attributed to high oxidation resistance of the CoP surface protected by the NCNHP.

Understanding the atomic diffusions at the nanoscale is important for controlling the synthesis and utilization of nanomaterials. Here, using in situ X-ray absorption spectroscopy coupled with theoretical calculations, we demonstrate a so far unexplored unidirectional diffusion from the Au shell to the Cu core in thermally alloying Cu@Au core@shell architecture of ca. 7.1 nm. The initial diffusion step at 423 K is found to be characterized by the formation of a diffusion layer composed of a Au-dilute substitutional CuAu-like intermetallic compound with short Cu-Au bond length (2.61 Å). The diffusion further happens by the migration of the Au atoms with large disorder into the interior Cu matrix at higher temperatures (453 and 553 K). These results suggest that the structural preference of a CuAu-like compound, along with the nanosized effect, plays a critical role in determining the atomic diffusion dynamics.

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au(13) clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure-property correlation and its strong dependence on the chemical environment for metal nanoclusters.

Understanding the formation process in the controlled synthesis of nanocrystals will lead to the effective manipulation of the morphologies and properties of nanomaterials. Here, in-situ UV-vis and X-ray absorption spectroscopies are combined to monitor the tracks of the nucleation pathways in the solution synthesis of platinum nanocrystals. We find experimentally that the control over nucleation pathways through changing the strength of reductants can be efficiently used to manipulate the resultant nanocrystal shapes. The in-situ measurements show that two different nucleation events involving the formation of one-dimensional "Pt(n)Cl(x)" complexes from the polymerization of linear "Cl(3)Pt-PtCl(3)" dimers and spherical "Pt(n)(0)" clusters from the aggregation of Pt(0) atoms occur for the cases of weak and strong reductants; and the resultant morphologies are nanowires and nanospheres, respectively. This study provides a crucial insight into the correlation between the particle shapes and nucleation pathways of nanomaterials.