Molecular catalysis for the steam reforming of ethanol

In this paper, the application of molecular catalysis for steam reforming of ethanol （SRE） is reviewed. Eight metals （Ni, Co, Cu Pt, Rh, Pd, Ir and Ru） have shown high catalytic activity for SRE. Among them Ni and Rh are very promising because of high d character in the metal bond and low metal-oxygen bonding （vs. metal-carbon）. They can effectively promote C-C bond cleavage in the rate-determining process during SRE. However, Rh is weak in water-gas-shift so that CH4 and CO become the main by-products at low reaction temperatures, while Ni catalysts suffer from rapid deactivation due to coking and sintering. Two low-temperature CO-free catalysts have been developed in our lab, namely Rh-Fe/Ca-Al2O3 and carbonyl-derived Rh-Co/CeO2, in which the presence of iron oxide or Co can promote water-gas-shift reaction and significantly improve the SRE performance. On the other hand, adding 3 wt% CaO to Ni/Al2O3 can greatly improve the catalyst stability because the Ca modification not only increases Ni concentration on the Ni/Ca-Al2O3 surface and 3d valence electron density, but also facilitates the water adsorption and coke gasification via water-gas-shift. The availability of abundant surface OH groups helps the formation and conversion of adsorbed formate intermediate. Hence, ethanol reaction on Ca-Al2O3-supported Ni, Pt, Pd and Rh catalysts are found to follow the formate-intermediated pathway, a new reaction pathway alternative to the traditional acetate-interrnediated pathway.

New tricks for an old dog: Visible light-driven hydrogen production from water catalyzed by fac-and mer-geometrical isomers of tris(thiosemicarbazide) cobalt(Ⅲ)

Increasing interest has been paid to the development of earth‐abundant metal complexes as promising surrogates of platinum for the electrocatalytically and photocatalytically driven hydrogen evolution reaction.In this work,we report on molecular H2‐evolving catalysts based on two octahedral complexes of cobalt thiosemicarbazide,fac‐[Co(Htsc)3]Cl3·3H2O(C1,Htsc=thiosemicarbazide)and mer‐[Co(Htsc)3]Cl3·4H2O(C2),which have facial(fac)and meridional(mer)geometry,respectively.Electrochemical studies confirmed that both C1and C2are active electrocatalysts in MeOH solution using acetic acid as the proton source,with the same overpotential of^640mV and TOF of^210s–1.The complex C1also exhibits electrocatalytic activity for hydrogen evolution reaction in aqueous media free of organic solvent with a moderate overpotential(560mV).Visible light‐driven hydrogen evolution experiments were carried out in combination with fluorescein as photosensitizer and triethylamine as sacrificial reductant in homogeneous environments.Our studies showed that both C1and C2can be used as efficient proton‐reduction catalysts in purely aqueous solution and have the same photocatalytic activities.A TOF of125h–1with a TON of900for photocatalytic H2generation using C1and C2in water were achieved for the noble‐metal‐free homogeneous system.It should be noted that this is the first reported study investigating the effect on the catalytic hydrogen production performance of using fac‐and mer‐isomers of molecular catalysts.

Highly selective and efficient electroreduction of CO_(2) in water by quaterpyridine derivative‐based molecular catalyst noncovalently tethered to carbon nanotubes

A disubstituted quaterpyridine based cobalt complex non‐covalently tethered to multiwalled carbon nanotube(MWCNT)substrate,forming a hybrid catalyst,Co‐qpyCOOH/CNT,catalyzed the conversion of CO_(2) to CO under aqueous conditions.At an optimal and uniform loading,it exhibited remarkable catalytic activity,near‐exclusive selectivity,and high stability towards the formation of CO.At a mere cathodic potential of−0.65 V versus RHE(η=0.54 V),it achieved a high partial current density of−6.7 mA/cm^(2) and a F.E.CO=100%.In addition,with 20 h of stable operation,hydrogen evolution remained practically undetected.Its hybrid structure due to noncovalent immobilization on MWCNT imparted the intrinsic activity and much‐needed stability in performance whereas‒COOH groups may stabilize the intermediates by acting as H‐bond donors,promoting catalytic activity.Tethering to a conductive solid substrate and tuning of the second sphere of coordination played an important role in its performance to achieve desired reduction product with high selectivity and activity.

Heavy-Atom-Free Photosensitizers for High-Yield CO_(2)-to-CO Conversion

Heavy-Atom-Free photosensitizers(HAFPs)with abundant resources showgreat potential to construct noble metal-free and high-yield CO_(2)photoreduction systems,but have rarely been achieved due to their poor intersystem crossing(ISC)efficiency.Herein,a library of HAFPs(B-1-B-8)were rationally designed by coupling various anthracene donors and boron dipyrromethene acceptors to break the short-lived excited state limitation of pure organic chromophores.The special orthogonal geometry between electron donor and acceptor contributes totriggering spin-orbit charge transfer-induced ISCs to achieve long-lived triplet and reduced states,which can facilitate consecutive intermolecular electron transfers to further boost CO_(2)reduction.Impressively,the reduced HAFP B-8 can efficiently sensitize iron catalysts to construct noble metal-free photocatalytic systems for highly efficient and selective CO_(2)-to-CO conversion with 1311μmol yield.Experimental and theoretical investigations clearly illustrate the structure-activity relationship,highlighting a new avenue to develop highly efficient organic photosensitizers to boost CO_(2)photoreduction.

Co porphyrin-based metal-organic framework for hydrogen evolution reaction and oxygen reduction reaction

Constructing molecule@support composites is an attractive strategy to realize heterogeneous molecular electrocatalysis.Herein,we synthesized metal-organic framework(MOF)-supported molecular catalysts for hydrogen evolution and oxygen reduction reaction(HER/ORR).Ligand exchange strategy was used to prepare molecule@support hybrids due to the same functional group.A series of hybrids were obtained using Co porphyrin(1)and different MOFs including MIL-88(Fe),MOF-5(NiCo)and UIO-66(Zr).The1@MOF-5(NiCo)had the best HER and ORR activity compared with 1@MIL-88(Fe)and 1@MOF-5(NiCo).These hybrids also exhibited tunable selectivity for ORR with four-electron process,which can be attributed to the synergistic effect of porphyrin molecules and MOFs.This work provides a possibility for molecular catalysts to improve activity of HER and tune selectivity of ORR.

Iodine-catalyzed N-sulfonylation of benzotriazoles with sodium sulfinates under mild conditions

A new and convenient procedure is developed for the preparation of N-sulfonylbenzotriazoles from sodium sulfinates and benzotriazoles using molecular iodine as catalyst via the S-N bond formation reaction. This catalytic radical sulfonylation proceeds efficiently in air at room temperature under neutral conditions, and in short reaction time, to afford the corresponding N-sulfonylbenzotriazoles in good yields, thus extending the catalytic application of molecular iodine in organic synthesis.