Seed-mediated synthesis of dendritic platinum nanostructures with high catalytic activity for aqueous-phase hydrogenation of acetophenone

This work reports a facile and efficient seed-mediated method for the synthesis of dendritic platinum （Pt） nanoparticles （NPs） at low temperatures of 55-60 ℃ in water, using L-ascorbic acid as a reducing agent and sodium citrate as a capping agent. It is found that the dendritic Pt NPs （10-150 nm） are composed of tiny Pt nanocrystals, which nucleate and grow through the introduced smaller Pt seeds with diameters of 3-5 nm. Further investigation shows that the dendritic Pt nanostructures display excellent catalytic performance in an aqueous-phase aromatic ketone hydrogenation reaction, including： （i） acetophenone conversion rate of 〉 90%, with smaller dendritic Pt NPs （10-46 nm） offering a higher conversion efficiency; （ii） high chemoselectivity toward carbonyl group （90.6%-91.5%）, e.g., the selectivity to l-phenylethanol is -90.1% with nearly 100% acetophenone conversion for 10 nm dendritic Pt NPs within 60 rain, under mild reaction conditions （20 ℃, 1.5 bar H2 pressure, and 1.5 tool% catalyst）. The high catalytic activity, selectivity and stability of the dendritic Pt nanostructures under the organic solvent-free conditions make them promising for many potential applications in green catalytic conversion of hydrophilic biomass derived compounds.

STUDIES ON THE SYNTHESIS OF BAIMUXINOL BY CATALYTIC HYDROGENATION OF DEHYDROBAIMUXINOL

Baimuxinol, a 4-hydroxymethyl agarofuran isolated from Aquilaria Sinensis, was synthsizd. The stereoselectivity of catalytic hydrogenation of dehydrobaimuxino and its derivatives was studied.

Direct synthesis of hydrogen peroxide over Pd nanoparticles embedded between HZSM-5 nanosheets layers

Direct synthesis of hydrogen peroxide(DSHP)was studied over Pd loaded on HZSM-5 nanosheets(Pd/ZN).Pd nanoparticles with average size of ca.4.3 nm were introduced into the adjacent nanosheet layers(thickness of ca.2.9 nm)by impregnation method.Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H2O2 among the prepared catalysts,together with highest formation rate of H2O2(38.0 mmol·(g cat)^-1·h^-1),1.9 times than that of Pd supported on conventional HZSM-5 zeolite(Pd/CZ-50).Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H2 dissociation,more BrΦnsted acid sites and stronger metal-support interaction which inhibited the dissociation of O-O bond in H2O2.The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching,leading to a better catalytic stability with 90%activity retained after 3 cycles,which was almost 3 times than that of Pd/CZ-50(30.4%activity retained).

Hydrogen evolution-assisted one-pot aqueous synthesis of hierarchical trimetallic PdNiRu nanochains for hydrazine oxidation reaction

A hydrogen evolution-assisted one-pot aqueous approach was developed for facile synthesis of trimetallic Pd Ni Ru alloy nanochain-like networks（Pd Ni Ru NCNs） by only using KBHas the reductant, without any specific additive（e.g. surfactant, polymer, template or seed）. The products were mainly investigated by transmission electron microscopy（TEM）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The hierarchical architectures were formed by the oriented assembly growth and the diffusioncontrolled deposition in the presence of many in-situ generated hydrogen bubbles. The architectures had the largest electrochemically active surface area（ECSA） of 84.32 mgPdthan Pd Ni nanoparticles(NPs,65.23 mgPd), Pd Ru NPs(23.12 mgPd), Ni Ru NPs（nearly zero）, and commercial Pd black(6.01 mgPd), outperforming the referenced catalysts regarding the catalytic characters for hydrazine oxygen reaction（HOR）. The synthetic route provides new insight into the preparation of other trimetallic nanocatalysts in fuel cells.

Effect of alkali metals on the performance of CoCu/TiO_2 catalysts for CO_2 hydrogenation to long-chain hydrocarbons

CoCu/TiO_2 catalysts promoted using alkali metals（Li, Na, K, Rb, and Cs） were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO_2 catalysts and the catalytic performance for CO_2 hydrogenation to long-chain hydrocarbons（C_（5＋））were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO_2 temperature-programmed desorption（TPD）, and H_2-TPD, the introduction of alkali metals could increase the CO_2 adsorption and decrease the H_2 chemisorption, which could suppress the formation of CH_4, enhance the production of C_（5＋）, and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO_2 catalyst provided the maximum C_（5＋） yield of 5.4%, with a CO_2 conversion of 18.4% and C_（5＋） selectivity of42.1%, because it showed the strongest basicity and a slight decrease in the amount of H_2 desorption;it also exhibited excellent catalytic stability of more than 200 h.

Electrocatalytic Activity of Ni/C Electrodes Prepared by Metal Vapor Synthesis For Hydrogen Evolution in Alkaline Solution

The metal vapor synthesis (MVS) methed was used to prepare activatedcarbon supported nickel electrode. The electrocatalytic activity of the electrode forhydrogen evolution reaction(HGR) in alkaline solution was studied. Cathodicpolarization curves showed the electrocatalytic activity of Ni/C electrode prepared byMVS method was higher than that of the one prepared by conventional method.

Synthesis and Structure Analysis of a Tripeptide Containing N-methyl Group Amino Acid

A convenient method of synthesizing a tripeptide-containing N-methyl group amino acid was developed using O-benzotriazole-N,N,N＇,N＇-tetramethyluronium-hexafluorophosphate as the condensing agent. The crystals of tripeptide had white needles belonging to the orthorhombic space group P2_12_12_1. The conformational preference for homochiral tripeptides with one N-methylated amide bond was also investigated. Crystal-structure analysis showed that homochiral tripeptides with an internal N-methylated amide bond preferred a trans-amide form, thereby giving the peptide β-fold characteristics. Intermolecular C-H···O and N-H···O hydrogen bonds linked the molecules into a one-dimensional chain and stabilized the structure.

Cobalt catalysts for Fischer–Tropsch synthesis： The effect of support,precipitant and pH value

In this report,Co-based catalysts supported on ZnO,Al_2O_3 and ZrO_2 as well as the ZrO_2 derived from different precipitants and different pH values were prepared by co-precipitation method.Their catalytic Fischer–Tropsch synthesis(FTS)performance was investigated in a fixed-bed reactor.The results revealed that Co catalyst supported on ZrO_2 exhibited better FTS catalytic performance than that supported on ZnO or Al_2O_3.For the Co/ZrO_2catalyst,different precipitants showed the following an activity order of NaOH>Na_2CO_3>NH_4OH,and the best pH value is 13.The catalysts were characterized by N_2adsorption–desorption,XRF,XRD,H_2-TPR,H_2-TPD and TEM.It was found that the main factor affecting the CO conversion of the catalyst was the amounts of low-temperature active adsorption sites.Moreover,the selectivity of C_5^+hydrocarbons had a positive relationship with the peak temperature of the weak hydrogen adsorption sites.The higher the peak temperature,the higher the C_5^+selectivity is.

RAMAN SPECTRA OF HYDROGEN ADSPECIES ON AMMONIA SYNTHESIS IRON CATALYST

Raman peaks at 1951 and 2165 cm^(-1) can be confirmed further by H_2/D_2 isotope exchange as H-adspecies on the doubly promoted iron catalyst for ammonia synthesis and are probably ascribed to two terminally adsorbed H-species.

Total entropy generation rate minimization configuration of a membrane reactor of methanol synthesis via carbon dioxide hydrogenation

The total entropy generation rate,internal exergy loss and exergy efficiency of the membrane reactor of methanol synthesis via carbon dioxide hydrogenation are compared,and the results show that the total entropy generation rate minimization is equivalent to the internal exergy loss minimization and the exergy efficiency maximization under the fixed inlet exergy.Therefore,this paper optimizes the membrane reactor with total entropy generation rate minimization as an optimization objective under a fixed methanol production rate.The optimal temperatures curves of exterior walls for three optimal membrane reactors with different boundary conditions are obtained by using optimal control theory and nonlinear programming.The influences of other geometric and operating parameters on optimization results of optimal membrane reactors are analyzed.The results indicate that when inlet temperatures of the reaction mixture and mixture in the permeable tube are unfixed,the optimizing curve of exterior wall temperature makes the total entropy generation rate of membrane reactor reduce by 12.39%compared with the total entropy generation rate of a reference membrane reactor with a linear exterior wall temperature.Decreasing the inlet molar flow rate of sweep gas and gas hourly space velocity and increasing inlet pressure of reaction mixture,the inlet pressure of mixture in the permeable tube and heat transfer coefficients are favorable for decreasing the total entropy generation rate in the membrane reactor.As the porosity of catalyst bed and reactor length increases,the minimum total entropy generation rate decreases first and then increases.From the perspective of engineering application,this paper establishes two membrane reactors(membrane reactor heated by three-stage furnaces of the same length and membrane reactor heated by threestage furnaces of different lengths),respectively.The minimum total entropy generation rates of the two reactors are reduced by11.67%and 11.79%compared with the total entropy generation rate in the reference membrane reactor,respectively.The obtained results are beneficial to the optimal design of energy-efficient membrane reactors.

Direct production of hydrogen peroxide over bimetallic CoPd catalysts:Investigation of the effect of Co addition and calcination temperature

A series of CoPd/KIT-6 bimetallic catalysts with various Co:Pd molar ratios at different calcination temperatures were prepared and used for the direct synthesis of H_(2)O_(2) from H_(2) and O_(2).These catalysts were characterized by nitrogen adsorption-desorption,low and wide-angle X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),scanning electron microscopy(SEM),elemental mapping and energy-dispersive X-ray(EDX)methods.It was found that the particle size,electronic interactions,morphology,and textural properties of these catalysts as well as their catalytic activity in the reaction of H_(2) with O_(2) were affected by Co addition and different calcination temperatures.Also,the results showed that while the H_(2)O_(2) selectivity depends on Pd^(2+) species,the H_(2) conversion is related to Pd0 active sites.Among these catalysts,CoPd/KIT-6 calcined at 350℃(CoPd/KIT-350 catalyst)showed the best catalytic activity with 50%of H_(2)O_(2) selectivity and 51%conversion of H_(2).

Direct synthesis of hydrogen peroxide on Pd nanosheets with edge decorated by Au nanoparticles

Direct synthesis of hydrogen peroxide from hydrogen and oxide(DSHP)is considered as a green pathway for H2O2 production because of the simple reaction route and 100%theoretical atom efficiency.Here,1.5 wt%Pd and 0.5 wt%Au were loaded on HZSM-5 nanosheets through sequential isovolumetric impregnation.TEM images and CO-TPD curves showed that Pd nanosheets were successfully synthesized between HZSM-5 nanosheets under zeolite confinement effect,and Au particles were loaded on the edge of Pd nanosheets and formed a structure that Pd nanosheets with edge decorated by Au nanoparticles(Au–Pd/ZN).The results showed that the selectivity for H2O2 could be reached around 60%in a 30 min reaction and the initial H2O2 productivity could reach 338.5 mmol gcat1 h1 on the Au–Pd/ZN catalyst.The enhanced selectivity and productivity could be related with high content of terrace sites and Au particles on the step sites of bimetallic nanosheets,in which both the terrace sites and the step sites replaced by Au particles showed higher dissociation activation energy for breaking the O–O bond than traditional step sites on Pd particles,inhibited the by-product reactions(2H2O2→2H2OþO2,2H2þO2→2H2O).

The effect of the concentration of plastic waste on the formation of reaction products of the Ti-PET system

The paper presents research results of the synthesis,phase composition,and structure of products obtained by highly exothermic reactions between Ti and C10H8O4mixture components,depending on the plastic waste concentration and Ti powder dispersiveness,density of initial samples,and synthesis medium.The dependence of the phase composition and structure of the synthesis products on the concentration of the polymer(plastic)component in the initial Ti-PET(C10H8O4)system was found.When the plastic waste content is 20 wt%to 25 wt%,synthesis products contain TiC0.5O0.5-TiC0.6-0.75particle agglomerates.Further growth in the polyethylene terephthalate content from 30 wt%to 45 wt%leads to the formation of synthesis products consisting of titanium carbide(TiC0.6-1.0).The gaseous byproduct composition of the exothermic reaction is investigated for the Ti--C10H8O4mixture composition.It is found that the gaseous by-product mostly contains hydrogen and carbon monoxide as well as impurities of different hydrocarbons(methane,acetylene,ethane,ethene)and carbon dioxide.The maximum adiabatic temperature of the gas combustion temperature is 2080℃,which demonstrates the possibility of using gas as a fuel for energy generation devices.Based on the data obtained,it is possible to create a basis for a new plastic waste technology to fabricate carbide-containing materials.

Highly dispersed Ag clusters for active and stable hydrogen peroxide production

The electrosynthesis of hydrogen peroxide(H2O2)from oxygen reduction reaction(ORR)via a two-electron pathway provides an appealing alternative to the energy-intensive anthraquinone route;however,the development of ORR with high selectivity and durability for H2O2 production is still challenging.Herein,we demonstrate an active and stable catalyst,composing of highly dispersed Ag nanoclusters on N-doped hollow carbon spheres(NC-Ag/NHCS),which can effectively reduce O2 molecules into H2O2 with a selectivity of 89%–91%in a potential range from 0.2 to 0.7 V(vs.reversible hydrogen electrode(RHE))in acidic media.Strikingly,NC-Ag/NHCS achieve a mass activity of 27.1 A·g^(−1) and a yield rate of 408 mmol·gcat.^(−1)·h^(−1) at 0.7 V,both of which are comparable with the best-reported results.Furthermore,NC-Ag/NHCS enable catalyzing H2O2 production with a stable current density over 48-h electrolysis and only about 9.8%loss in selectivity after 10,000 cycles.Theoretical analyses indicate that Ag nanoclusters can contribute more electrons to favor the protonation of adsorbed O2,thus leading to a high H2O2 selectivity.This work confirms the great potential of metal nanocluster-based materials for H2O2 electrosynthesis under ambient conditions.

单原子钌分散的TiO_(2)促进高效水氧化产过氧化氢

电催化两电子水氧化为分布式合成H_(2)O_(2)提供了一个有效的途径.但是由于缺乏合适的阳极电催化剂,通过两电子水氧化合成H_(2)O_(2)难以兼得高选择性和高产率.本文将钌单原子可控地引入到TiO_(2)中,用于促进高效水氧化产H_(2)O_(2).研究发现,钌单原子的引入优化了材料对含氧中间体的吸附,在获得高电流密度的同时促进了H_(2)O_(2)产生.具体来说,通过对钌掺杂浓度的调控,所合成催化剂在120 mA cm^(-2)的电流密度下实现了62.8%的法拉第效率,并且H_(2)O_(2)产率高达24.2μmol min-1cm^(-2)(10 min内H_(2)O_(2)积累超过400 ppm).本文不仅证明了在高电流密度下高效率产H_(2)O_(2)的可能性,同时也验证了在电催化水氧化过程中调节中间体吸附的重要性.