摘要: The Ni-W/SBA-15 catalysts prepared by incipient-wetness impregnation method and controlled by the pH value were developed. Potassium hydroxide and citric acid regarded as the pH value regulators were added to the solution before impregnation to provide an acidic or basic condition at different pH values (0.83, 1.00, 3.09, 5.00, 7.03, 8.97 and 11.0). The 74.5% yield of total low carbon (C2, 3) polyols including ethylene glycol (EG), 1, 2-propylene glycol (1, 2-PG) and glycerol (Gly) was obtained over 10%Ni-20%W/SBA-15 catalyst prepared at pH value of 1.00 and 518 K under H2 pressure of 5.0 MPa. Furthermore, the physical properties of this series of nickel-tungsten catalysts were characterized by BET and SEM. The results demonstrated that the catalysts showed excellent thermal stability and the surface area was mainly in range of 330-450 m2/g. The particles had a good dispersion on the surface of SBA-15 but some aggregations were existed which could be characterized by TEM and SEM-EDX. However, the reduction of metallic oxides especially for NiO was obviously influenced by pH value control and some metallic species characterized by XRD. According to XRD results, the impregnation pH value influenced the reduction of NiO and the phase states of nickel and tungsten species.
摘要: Dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) is one of the pivotal reactions in conversion of biomass towards valuable platform compounds. In this work, Nb/SBA-15 was prepared via incipient wetness impregnation with self-made SBA-15 as support; Nb/SBA-15 was further treated with phosphoric acid and calcined at 450℃, to obtain the Nb-P/SBA-15 catalyst. The Nb-P/SBA-15 catalyst was characterized by SEM, TEM, BET, XRD and NH3-TPD; its performance in the dehydration of fructose to 5-HMF was then investigated. The results indicate that the microscopic structure of SBA-15 is well preserved in Nb/SBA-15 with an internal channel diameter of about 10 nm and the niobic species are highly dispersed on the surface of the channels; the wall of channels became thinner after impregnation of Nb and treatment with phosphoric acid. After the treatment with phosphoric acid, the weak acid sites are increased, moreover, the medium and strong acidic sites are generated in Nb-P/SBA-15; as a result, for the dehydration of fructose in a water/MIBK biphasic system, Nb-P/SBA-15 exhibits higher catalytic activity and selectivity to 5-HMF. By reaction at 160℃ for 1.5 h, with a water/MIBK volume ratio of 1/2, the conversion of fructose and the yield of 5-HMF reach 96.1% and 92.6%, respectively. Moreover, the Nb-P/SBA-15 catalyst also exhibits excellent stability in view of water tolerance; it still demonstrates high catalytic activity and selectivity to 5-HMF even after successive recycling for four times.
摘要: A Pt/HZSM-5 catalyst was prepared by atomic layer deposition (ALD) for aqueous-phase hydrogenation of levulinic acid (LA) to valeric acid (VA). 5Pt/HZSM-5 produced with 5 cycles of Pt ALD was identified as a highly active and stable bifunctional catalyst, and a high yield of VA (91.4%) was achieved in aqueous solution. A close interaction between Pt and acid sites of HZSM-5 is favor for the selective generation of VA. The microporous structure and the acid sites of HZSM-5 were not changed after Pt ALD, and some Pt nanoparticles were located in the micropore channel of HZSM-5. This reveals that the Pt ALD has the advantage to protect the structure of zeolite. The average particle size of Pt nanoparticles, electric state of surface Pt, and surface acid sites are nearly not changed with the increase of Pt ALD cycle number. However, the ratio of Pt in the pore channel to that out of the pore decreases with the increase of ALD cycle numbers, resulting in a decrease of TOF of VA yield. For comparison, Pt nanoparticles supported on HZSM-5 were also produced by impregnation. But the pore structure of HZSM-5 was damaged, and more micropore were formed by impregnation method for Pt loading. Moreover, it exhibited very low catalytic activity, selectivity of VA, and stability.
摘要: A series of Ce-La/MgAl2O4-x catalysts were prepared by the incipient wetness impregnation method and characterized by BET, XRD, H2-TPR, CO-TPR and in situ FT-IR. The results demonstrate that the catalyst with a Mg/Al molar ratio of 0.5 yields the most uniform dispersion of CeO2 and greatly enhances formation of Ce-O-La solid solution, resulting in the increase of oxygen vacancy and surface Ce3+ content. Thereby, the synergistic effect between surface Ce3+ and oxygen vacancy gives rise to the best catalytic performance of NO reduction. Moreover, introduction of Mg species suppresses tranformation of CeO2 to Ce(SO4)2/Ce2(SO4)3 and then improves the SO2 resistance performance of Ce-La/MgAl2O4-0.5.