Bimetallic CoNi single atoms supported on three-dimensionally ordered mesoporous chromia:highly active catalysts for n-hexane combustion

Developing the alternative supported noble metal catalysts with low cost,high catalytic efficiency,and good resistance toward carbon dioxide and water vapor is critically demanded for the oxidative removal of volatile organic compounds(VOCs).In this work,we prepared the mesoporous chromia-supported bimetallic Co and Ni single-atom(Co_(1)Ni_(1)/meso-Cr_(2)O_(3))and bimetallic Co and Ni nanoparticle(Co_(NP)Ni_(NP)/mesoCr_(2)O_(3))catalysts adopting the one-pot polyvinyl pyrrolidone(PVP)-and polyvinyl alcohol(PVA)-protecting approaches,respectively.The results indicate that the Co_(1)Ni_(1)/meso-Cr_(2)O_(3)catalyst exhibited the best catalytic activity for n-hexane(C_(6)H_(14))combustion(T_(50%)and T_(90%)were 239 and 263℃ at a space velocity of 40,000 mL g^(-1)h^(-1);apparent activation energy and specific reaction rate at 260℃ were 54.7 kJ mol^(-1)and 4.3×10^(-7)mol g^(-1)_(cat)s^(-1),respectively),which was associated with its higher(Cr^(5+)+Cr^(6+))amount,large n-hexane adsorption capacity,and good lattice oxygen mobility that could enhance the deep oxidation of n-hexane,in which Ni_(1) was beneficial for the enhancements in surface lattice oxygen mobility and low-temperature reducibility,while Co_(1) preferred to generate higher contents of the high-valence states of chromium and surface oxygen species as well as adsorption and activation of n-hexane.n-Hexane combustion takes place via the Mars van Krevelen(MvK)mechanism,and its reaction pathways are as follows:n-hexane→olefins or 3-hexyl hydroperoxide→3-hexanone,2-hexanone or 2,5-dimethyltetrahydrofuran→2-methyloxirane or 2-ethyl-oxetane→acrylic acid→CO_x→CO_(2)and H_(2)O.

STUDIES ON THE STATE OF PALLADIUM AND HYDROGENATION ACTIVITY OF RESIN SUPPORTED PALLADIUM──TIN OXIDE CATALYSTS

Several Pd--SnO2/ D3520 and Pd--PbO / D3520 catalysts with Pd/ D3J20, SnO2 / D3520 and PbO / D3520 catalysts as rference were studied by means of IR and XPS. Interaction between Pd and the second metal or between metal and support was observed. Results show that there is a strong interaction between Pd and the second metal, but there is not an obvious interaction between metal and support. The active constituent is Pd￣0. Hydrogenation activity of the catalysts is altered because of the interaction between Pd and the second,metal.The activity of the catalysts for hydrogenation has relation to outer layer valence electron density of Pd.

Green process for hydrogenation of methyl ricinoleate to methyl 12-hydroxystearate over diatomite supported Cu/Ni bimetallic catalyst

A series of diatomite supported Cu/Ni bimetallic catalysts were prepared using the co-impregnation method to improve the efficiency and selectivity toward methyl 12-hydroxystearate in the hydrogenation of methyl ricinoleate.The catalysts were characterized using X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy and energy dispersive X-ray spectroscopy(SEM-EDS),X-ray photoelectron spectroscopy(XPS)and temperature programmed reduction(H2-TPR).All the characterization results verified the formation of highly dispersed Cu/Ni alloy on support.Moreover,by subtly regulating the Ni/Cu molar ratio as well as the reaction parameters,the hydrogenation of methyl ricinoleate to methyl 12-hydroxystearate proceeded efficiently and selectively,affording 97%yield of methyl 12-hydroxystearate and nearly equivalent conversion of methyl ricinoleate under 2 MPa H2 pressure and at 130 C in 4 h with only 1 wt%of the catalyst Ni7Cu1/diatomite(based on methyl ricinoleate).Besides,the supported Cu–Ni bimetallic catalyst is stable during recycle and reuse.After five cycles of reuse,much catalytic activity is still preserved.Therefore,this low-cost and stable bimetallic catalyst would be promising for the hydrogenation of methyl ricinoleate to methyl 12-hydroxystearate,representing an example of green catalysis for efficiently conversion of biomass to value-added chemicals and materials.

Zn-Co bimetallic supported ZSM-5 catalyst for phosgene-free synthesis of hexamethylene–1,6–diisocyanate by thermal decomposition of hexamethylene–1,6–dicarbamate

A set of mono-and bimetallic（Zn-Co） supported ZSM-5 catalysts was first prepared by PEG-additive method. The physicochemical properties of the catalysts were investigated by FTIR, XPS, XRD, N2adsorption-desorption measurements, SEM, EDS and NH3-TPD techniques. The physicochemical properties showed that the Zn Co2O4 spinel oxide was formed on the ZSM-5 support and provided effectual synergetic effect between Zn and Co species for the bimetallic catalyst. Furthermore, bimetallic supported ZSM-5 catalyst exhibited weak, moderate and strong acidic sites, while the monometallic supported ZSM-5 catalyst showed only weak and moderate or strong acidic sites. Their catalytic performances for thermal decomposition of hexamethylene–1,6–dicarbamate（HDC） to hexamethylene–1,6–diisocyanate（HDI） were then studied. It was found that the bimetallic supported ZSM-5 catalysts,especially Zn-2Co/ZSM-5 catalyst showed excellent catalytic performance due to the good synergetic effect between Co and Zn species, which provided a suitable contribution of acidic sites. HDC conversion of 100% with HDI selectivity of 91.2% and by-products selectivity of 1.3% could be achieved within short reaction time of 2.5 h over Zn-2Co/ZSM-5 catalyst.