Self-assembled three-dimensional carbon networks with accessorial Lewis base sites and variational electron characteristics as efficient oxygen reduction reaction catalysts for alkaline metal-air batteries

Heteroatom-doped carbon has been demonstrated to be one of the most promising non-noble metal catalysts with high catalytic activity and stability through the modification of the electronic and geometric structures.In this study,we develop a novel solvent method to prepare interconnected N,S co-doped three-dimensional（3D）carbon networks with tunable nanopores derived from an asso-ciated complex based on melamine and sodium dodecylbenzene sulfonate（SDBS）.After the intro-duction of silica templates and calcination,the catalyst exhibits 3D networks with interconnected 50-nm pores and partial graphitization.With the increase of the number of Lewis base sites caused by the N doping and change of the carbon charge and spin densities caused by the S doping,the designed N,S co-doped catalyst exhibits a similar electrochemical activity to that of the commercial 20-wt%Pt/C as an oxygen reduction reaction catalyst.In addition,in an aluminum-air battery,the proposed catalyst even outperforms the commercial 5-wt%Pt/C catalyst.Both interconnected porous structures and synergistic effects of N and S contribute to the superior catalytic perfor-mance.This study paves the way for the synthesis of various other N-doped and co-doped carbon materials as efficient catalysts in electrochemical energy applications.

The effect of FER zeolite acid sites in methanol-to-dimethyl-ether catalytic dehydration

In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.

Zr（Ⅳ） surface sites determine CH3OH formation rate on Cu/ZrO2/SiO2-CO2 hydrogenation catalysts

Cu/ZrO2/SiO2 are efficient catalysts for the selective hydrogenation of CO2 to CH3OH. In order to understand the role of ZrO2 in these mixed-oxides based catalysts, in situ X-ray absorption spectroscopy has been carried out on the Cu and Zr K-edge. Under reaction conditions, Cu remains metallic, while Zr is present in three types of coordination environment associated with 1) bulk ZrO2, 2) coordinatively saturated and 3) unsaturated Zr(Ⅳ) surface sites. The amount of coordinatively unsaturated Zr surface sites can be quantified by linear combination fit of reference X-Ray absorption near edge structure (XANES) spectra and its amount correlates with CH3OH formation rates, thus indicating the importance of Zr(Ⅳ) Lewis acid surface sites in driving the selectivity toward CH3OH. This finding is consistent with the proposed mechanism, where CO2 is hydrogenated at the interface between the Cu nanoparticles that split H2 and Zr(Ⅳ) surface sites that stabilizes reaction intermediates.

Deactivation mechanism of acetone to isobutene conversion over Y/Beta catalyst

The conversion of acetone derived from biomass to isobutene has attracted extensive attentions.In comparison with Brønsted acidic catalyst,Lewis acidic catalyst could exhibit a better catalytic performance with a higher isobutene selectivity.However,the catalyst stability remains a key problem for the long-running acetone conversion and the reasons for catalyst deactivation are poorly understood up to now.Herein,the deactivation mechanism of Lewis acidic Y/Beta catalyst during the acetone to isobutene conversion was investigated by various characterization techniques,including acetone-temperature-programmed surface reaction,gas chromatography-mass spectrometry,in situ ultraviolet-visible,and ^(13)C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy.A successive aldol condensation and cyclization were observed as the main side-reactions during the acetone conversion at Lewis acidic Y sites.In comparison with the low reaction temperature,a rapid formation and accumulation of the larger cyclic unsaturated aldehydes/ketones and aromatics could be observed,and which could strongly adsorb on the Lewis acidic sites,and thus cause the catalyst deactivation eventually.After a simple calcination,the coke deposits could be easily removed and the catalytic activity could be well restored.

Regulating Lewis Acid-Base Sites over Fenton System for Enhancing Degradation of Pollutants in Saline and Buffered Wastewater

The saline and buffered environment in actual wastewater imposes higher demands on Fenton and Fenton-like catalytic systems.This study developed a MoS_(2)co-catalytic Fe_(2)O_(3)Fenton-like system with controllable Lewis acid-base sites,achieving efficient treatment of various model pollutants and actual industrial wastewater under neutral buffered environment.The acidic microenvironment structured by the edge S sites(Lewis basic sites)in the MoS_(2)/Fe_(2)O_(3)catalyst is susceptible to the influence of Lewis acidic sites constructed by Mo and Fe element,affecting catalytic performance.Optimizing the ratio of precursor amounts ensures the stable presence of the acidic microenvironment on the surface of catalyst,enabling the beneficial co-catalytic effect of Mo sites to be realized.Furthermore,it transcends the rigid constraints imposed by the Fenton reaction on reaction environments,thereby expanding the applicability of commonplace oxides such as Fe_(2)O_(3)in actual industrial water remediation.

FCF-LDH/BiVO_(4)with synergistic effect of physical enrichment and chemical adsorption for efficient reduction of nitrate

Photoelectrochemical NO_(3)^(-)reduction(PEC NITRR)not only provides a promising solution for promoting the global nitrogen cycle,but also converts NO_(3)^(-)to the important chemicals(NH_(3)).However,it is still a great challenge to prepare catalysts with excellent NO_(3)^(-)adsorption/activation capacity to achieve high NITRR.Herein,we designed a novel Fe^(2+)~Cu^(2+)Fe^(3+)LDH/BiVO_(4)(FCF-LDH/BVO)catalyst with synergistic effect of chemical adsorption and physical enrichment.Fe^(2+)in FCF-LDH/BVO provides the rich Lewis acid sites for the adsorption of NO_(3)^(-),and the appropriate layer spacing of FCF-LDH further promotes the physical enrichment of NO_(3)^(-)in its interior,thus realizing the effective contact between NO_(3)^(-)and active sites(Fe^(2+)).FCF-LDH/BVO showed excellent NH_(3)production performance(FE_(NH_(3))=66.1%,r_(NH_(3))=13.8μg h^(-1)cm^(-2))and selectivity(FE_(NO_(2)^(-))=2.5%,r_(NO_(2)^(-))=4.9μg h^(-1)cm^(-2))in 0.5 mol L^(-1)Na_(2)SO_(4)electrolyte.In addition,FCF-LDH/BVO maintains the desirable PEC stability for six cycle experiments,showing great potential for practical application.The^(14)NO_(3)^(-)and^(15)NO_(3)^(-)isotope test provides strong evidence for further verification of the origin of N in the generated NH_(3).This LDH catalyst has a great potential in PEC removal of NO_(3)^(-)from groundwater.

Integrating Homogeneous and Heterogeneous Catalysis in a Copper Nanocluster with Lewis Acid–Base Sites for Chemical Conversion of CO_(2) and Propargylamine

It remains a significant challenge to develop a catalyst that merges the advantages of homogeneous and heterogeneous catalysis with high reactivity and great recyclability.Herein,an atomically precise Cu_(6)-NH_(2) nanocluster with distorted octahedral Cu_(6) core and NH_(2)-functionalized ligands has been developed as the first homo/heterogeneous catalyst to catalyze the cyclization reaction of propargylic amines with carbon dioxide(CO_(2))under mild conditions.As a homogeneous catalyst,Cu_(6)-NH_(2) shows excellent catalytic activity with high turnover frequency due to highly accessible active sites.The definite coordination geometry and homogeneity nature of active centers make it convenient to investigate the structure–activity relationship at the atomic level through experiments and theory calculations.In addition,the nanocluster exhibits excellent stability,great recrystallizability,and reusability in five catalytic cycles,in which its catalytic performance has no obvious decrease.Moreover,Cu_(6)-NH_(2) incorporates Lewis acid and base sites in metal and ligand,respectively,which can promote catalytic efficiency in a synergistic effect in the absence of any cocatalysts.Importantly,Cu_(6)-NH_(2) can realize direct conversion of CO_(2) in simulated flue gas into oxazolidinones with high efficiency.The metal-ligand cooperative effect and integrated advantages of homogeneous and heterogeneous catalysis would provide new perspectives to achieve advanced metal nanocluster catalysts for CO_(2) conversion.

Performances of CuSO_4/TiO_2 catalysts in selective catalytic reduction of NO_x by NH_3

A series of CuSO4/TiO2 catalysts were prepared using a wet impregnation method.The activity of each sample in the selective catalytic reduction of NO by NH3（NH3-SCR） was determined.The effects of SO2 and H2O,and their combined effect,on the activity were examined at 340 ℃ for 24 h.The catalysts were characterized using N2 adsorption-desorption,X-ray diffraction,X-ray photoelectron spectroscopy,temperature-programmed reduction of H2（H2-TPR）,temperature-programmed desorption of NH3（NH3-TPD）,and in situ diffuse-reflectance infrared Fourier-transform spectroscopy（DRIFTS）.The CuSO4/TiO2 catalysts had good activities,with low production of N2O above 340 ℃.SO2 or a combination of SO2 and H2O had little effect on the activity,and H2O caused only a slight decrease in activity during the experimental period.The NH3-TPD and H2-TPR results showed that CuSO4 increased the amounts of acid sites and adsorbed oxygen on the catalyst.In situ DRIFTS showed that the NH3-SCR reaction on the CuSO4/TiO2 catalysts followed an Eley-Rideal mechanism.The reaction of gaseous NO with NH3 adsorbed on Lewis acid sites to form N2 and H2O could be the main reaction pathway,and oxygen adsorption might favor this process.

Depolymerization and hydrodeoxygenation of lignin to aromatic hydrocarbons with a Ru catalyst on a variety of Nb-based supports

Efficient conversion of lignin to aromatic hydrocarbons via depolymerization and subsequent hydrodeoxygenation is important.Previously,we found that NbOx species played a key role in the activation and cleavage of C-O bonds in lignin and its model compounds.In this study,commercial niobic acid(HY-340),niobium phosphate(NbPO-CBMM)and lab-made layered niobium oxide(Nb2O5-Layer)were chosen as supports to study the effect of Brosted and Lewis acids on the activation of C-O bonds in lignin conversion.A variety of Ru-loaded,Nb-based catalysts with different Ru particle sizes were prepared and applied to the conversion of p-cresol.The results show that all the Ru/Nb-based catalysts produce high mole yields of C7-C9 hydrocarbons(82.3%-9.1%).What's more,Ru/Nb2O5-Layer affords the best mole yield of C7-C9 hydrocarbons and selectivity for C7-C9 aromatic hydrocarbons,of up to 99.1% and 88.0%,respectively.Moreover,it was found that Lewis acid sites play important roles in the depolymerization of enzymatic lignin into phenolic monomers and the cleavage of the C-O bond of phenols.Additionally,the electronic state and particle size of Ru are significant factors which influence the selectivity for aromatic hydrocarbons.A partial positive charge on the metallic Ru surface and a smaller Ru particle size are beneficial in improving the selectivity for aromatic hydrocarbons.

Synergistic Lewis acid-base sites of ultrathin porous Co_(3)O_(4)nanosheets with enhanced peroxidase-like activity

Surface Lewis acid-base sites in crystal structure may influence the physicochemical properties and the catalytic performances in nanozymes.Understanding the synergistic effect mechanism of Co_(3)O_(4)nanozymes towards substances(3,3’,5,5’-tetramethylbenzidine(TMB)and hydrogen peroxide(H2O2))induced by surface Lewis acid-base sites is important to enhance the efficiency for peroxidase-like reaction.Herein,ultrathin porous Co_(3)O_(4)nanosheets with abundant Lewis acid-base sites were prepared by sodium borohydride(NaBH4)reduction treatment,which exhibited high-efficiency peroxidase-like activity compared with original Co_(3)O_(4)nanosheets.The Lewis acid-base sites for ultrathin porous Co_(3)O_(4)nanosheets nanozyme were owing to the coordination unsaturation of Co ions and the formation of defect structure.Ultrathin porous Co_(3)O_(4)nanosheets had 18.26-fold higher catalytic efficiency(1.27×10^(-2)s^(-1)·mM^(-1))than that of original Co_(3)O_(4)(6.95×10^(-4)s^(-1)·mM^(-1))in oxidizing TMB substrate.The synergistic effect of surface acid and base sites can enhance the interfacial electron transfer process of Co_(3)O_(4)nanosheets,which can be a favor of absorption substrates and the generation of reactive intermediates such as radicals.Furthermore,the limit of detection of hydroquinol was 0.58μM for ultrathin porous Co_(3)O_(4)nanosheets,965-fold lower than original Co_(3)O_(4)(560μM).Besides,the linear range of ultrathin porous Co_(3)O_(4)nanosheets was widely with the concentration of 5.0-1,000μM.Colorimetric detection of hydroquinol by agarose-based hydrogel membrane was provided based on excellent peroxidase-like properties.This study provided insights into designing high-performance nanozymes for peroxidase-like catalysis via a strategy of solid surface acid-base sites engineering.

Conversion of ethanol to 1,3-butadiene over Ag-ZrO_(2)/SiO_(2) catalysts:The role of surface interfaces

A series of Ag-ZrO_(2)/SiO_(2) catalysts with different metal-support interfaces were synthesized in an effort to elucidate the roles of specific interfaces in controlling the ethanol to 1,3-butadiene conversion and selectivity.According to the results of detailed characterizations(e.g.CO/pyridine-DRIFTS,XPS,TEM,NH3-TPD,and ^(1)H MAS NMR),it was found that the Ag-O-Si interfaces significantly enhanced the dehydrogenation of ethanol while the presence of ZrO_(2) improved the interaction between Ag and ZrO_(2)/SiO_(2),creating more Ag^(δ+)active sites.The high dispersion of ZrO_(2) on SiO_(2) generated abundant Zr-O-Si interfaces with medium and weak Lewis acidity,promoting the condensation of acetaldehyde to crotonaldehyde.These Zr-O-Si interfaces in close interaction with Ag^(δ+)species played a critical role in the enhanced H transfer during the MPV reduction of crotonaldehyde to crotyl alcohol.The synergies among the interfaces resulted in retarded ethanol dehydration reactivity,balanced ethanol dehydrogenation and condensation reactions,and a subsequent high 1,3-butadiene yield.

Effect of iridium loading on HZSM-5 for isomerization of n-heptane

The effect of iridium loading on the properties and catalytic isomerization of n-heptane over Ir-HZSM-5 is studied. Ir-HZSM-5 was prepared by impregnation method and subjected to isomerization process in the presence of flowing hydrogen gas. XRD and BET studies show that the presence of iridium stabilizes the crystalline structure of HZSM-5, leading to more ordered framework structure and larger surface area. TGA and FTIR results substantiate that iridium species interacts with OH group on the surface of HZSM-5. Pyridine FT-IR study verifies the interaction between iridium and surface OH group slightly increased the Bro¨nsted and Lewis acid sites without changing the lattice structure of HZSM-5. The presence of iridium and the increase of strong Lewis acid sites on HZSM-5 were found to bring an increase about 4.1%, 33.2% and 11.8% in conversion, selectivity and yield of n-heptane isomerization, respectively.

Some insight on the structure/activity relationship of metal nanoparticles in Cu/SiO2 catalysts

The activity of two Cu/SiO2 catalysts prepared by the chemisorption hydrolysis technique has been tested in the hydrogenation reaction of 3-methyl-cyclohexanone. Both catalysts were found to be very active at 60 ℃ and 1 atm of H2. Characterization of the materials by FT-IR of adsorbed CO and TEM put in light the presence of well formed Cu cristallites. By assuming a cuboctahedral model we could show that the hydrogenation activity is linked to high coordination sites on the metal particle. A comparison is also reported with a sample prepared by ammonia evaporation that was found to be inactive in the hydrogenation reaction under the same experimental conditions.

Effect of x-alumina addition on H_2S oxidation properties of pure and modified y-alumina

The influence of the textural and acidic properties ofγ‐Al2O3,(γ+χ)‐Al2O3,and?‐Al2O3on the catalytic activity,selectivity,and stability of direct H2S oxidation has been studied.A comparison of the H2S‐to‐S conversion effectiveness of aluminas with their acidic properties(identified by Fourier transform infrared spectroscopy and temperature programmed desorption of NH3)shows that H2S adsorption occurs predominantly on weak Lewis acid sites(LAS).γ‐Alumina samples containing aχ‐phase and/or modified Mg2+ions have a greater concentration of weak LAS and exhibit greater catalytic activity.When alumina is treated with a sulfuric acid solution,strong LAS appear and the number of LAS decreases significantly.Modification of alumina with hydrochloric acid has a limited effect on LAS strength.Weak LAS are retained and double in number compared to that present in the unmodified alumina,but the treated sample has Al?Cl bonds.Alumina samples modified by sulfate and chloride anions exhibit poor catalytic activity in H2S oxidation.

A Novel Co(Ⅱ)-organic Framework with Multiple Active Sites for Selective Gas Adsorption

A novel metal-organic framework[Co(BTTA)(H_(2)O)_(2)]_(n)(FJI-H_(2)4)has been prepared from H_(2)BTTA ligand and CoCl_(2),and its structure was determined by single-crystal X-ray diffraction,thermogravimetric analysis,and Fourier transform infrared spectroscopy.It has relatively narrow pores and high density of open metal ions and free Lewis base sites.Gas adsorption tests demonstrate that FJI-H_(2)4 has moderate CO_(2)(34.0 cm^(3)·g^(–1))and C_(2)H_(2)(53.0 cm^(3)·g^(–1))adsorption capacity,but displays high selectivity of CO_(2)/N_(2)(87)and C_(2)H_(2)/CH_(4)(66)under ambient conditions(298 K,1 atm),which may be attributed to its relatively narrow pores and polar environment.This work will provide a potential strategy for preparing practical porous metal-organic frameworks for gas adsorption and purification.

Catalytic ozonation performance and surface property of supported Fe304 catalysts dispersions

Fe304 was supported on mesoporous A12O3 or SiO2 （50 wt.%） using an incipient wetness impregnation method, and Fe304/A12O3 exhibited higher catalytic efficiency for the degradation of 2,4-dichlorophenoxyace- tic acid andpara-chlorobenzoic acid aqueous solution with ozone. The effect and morphology of supported Fe304 on catalytic ozonation performance were investigated based on the characterization results of X-ray diffraction, X-ray photoelectron spectroscopy, BET analysis and Fourier transform infrared spectroscopy. The results indicated that the physical and chemical properties of the catalyst supports especially their Lewis acid sites had a significant influence on the catalytic activity. In comparison with SiO2, more Lewis acid sites existed on the surface of A12O3, resulting in higher catalytic ozonation activity. During the reaction process, no significant Fe ions release was observed. Moreover, Fe304/A12O3 exhibited stable structure and activity after successive cyclic experiments. The results indicated that the catalyst is a promising ozonation catalyst with magnetic separation in drinking water treatment.

A Sulfonate-based Metal-organic Framework for the Transformation of CO and Epoxides into Cyclic Carbonates

An interesting metal-organic framework(MOF) PFC-31 was synthesized by a simple solvothermal reaction. X-ray crystallography reveals that PFC-31 crystallizes in monoclinic system, space group P21/c with a = 6.8410(17), b = 20.123(5), c = 7.689(2) ?, β = 104.239(7)°, V = 1026.0(5) ?3, Z = 2, C16 H22 CuN4 O8 S2, Mr = 526.03, μ = 1.322 mm-1, Dc = 1.703 g/cm3, F(000) = 542, GOOF = 1.214, R = 0.0975 and w R = 0.2324. According to X-ray analysis, PFC-31 shows one-dimensional chain constructed by Cu(Ⅱ) centers coordinating with two pyridine groups, two sulfonate groups and two DMF molecules. Owing to the orderly functionalized sulfonate group and Lewis metal sites, PFC-31 exhibits good catalytic capability for CO2 cycloaddition of epoxide under normal pressure and temperature.

A low-temperature synthesis-induced defect formation strategy for stable hierarchical porous metal–organic frameworks

A stable hierarchical porous metal-organic framework PCN-56 with abundant Lewis acid sites(denoted as Defective-PCN-56) was synthesized by the low-temperature synthesis-induced defect formation method.The existence of mesopore in structure was confirmed by N2 sorption isotherm and the successful encapsulation of large dye molecules.The Defective-PCN-56 has higher loading capacity toward anti-cancer drug Doxo compared with that of "nearly ideal-crystal"(denoted as Ideal-PCN-56)synthesized at high temperature,showing potential application as drug carrier.The low-temperature synthesis-induced defect formation strategy presented here provides a new and facile way to synthesize stable MOFs with the combination of intrinsic micropore and additional mesopore as well as abundant Lewis acid sites.

Ln-substituted polytungstates as efficient hetergeneous catalysts for Knoevenagel condensation reaction

Three isomorphic polytungstates,CsgK_(18)H_(10){[Sm_(2)(H_(2)O)_(4)W_(4)O_(10)(AsW_(9)0_(33))3]_(2)(N(CH_(2)PO_(3))_(2))}:46.5H_(2)O(1),CS_(10)K_(9)H_(18){[Eu_(2)(H_(2)O)_(4)W_(4)O_(10)(AsW_(9)0_(33))_(3)]_(2)(N(CH_(2)PO_(3))_(2))}.41.5H_(2)O(2),Cs_(10)K_(9)H_(18){[Gd_(2)(H_(2)O)_(4)W_(4)O_(10)(AsW_(9)O_(33))_(3)]_(2)(N(CH_(2)PO_(3))_(2))}:46H_(2)O(_(3)),have been successfully synthesized and characterized by routine methods,and demonstrated excellent catalytic activities in Knoevenagel condensation reaction as heterogeneous catalysts.Notably,catalyst 1 achieved higher reaction activity than catalysts 2 and 3,where a satisfactory reaction yield(95%)and high TON value(6380)could be obtained at moderate reaction condition.In addition,in the scale-up experiment,with the help of catalyst 1,7.8g benzaldehyde and 5.7g ethyl cyanoacetate could transform into corresponding condensation product with a satisfactory yield(83%)and impressive TON value(13.883).

Enhanced Catalysis of Pt_(3) Clusters Supported on Graphene for N–H Bond Dissociation

We report an in-depth study of catalytic N–H bond dissociation with typical platinum clusters on gra-phene supports.Among all the pristine graphene-and defective graphene-supported Pt clusters of different sizes that were studied,the Pt_(3)/G cluster possesses the highest reactivity and lowest activa-tion barriers for each step of N–H dissociation in the decomposition of ammonia.