Huayan Liu

Alkali-metal-modified ZSM-5 zeolites for improvement of catalytic dehydration of lactic acid to acrylic acid

Abstract Various ZSM-5 zeolites modified with alkali metals (Li, Na, K, Rb, and Cs) were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid (LA) to acrylic acid (AA). The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, temperature-programmed desorptions of NH 3 and CO 2 , pyridine adsorption spectroscopy, and N 2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities (LHSVs) to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions (40 wt% LA aqueous solution, 365 °C, and LHSV 2 h −1 ).

Preparation of Highly Loaded LaMnOx/SBA-15 Catalyst and Its Toluene Combustion Performance

A highly loaded LaMnOx/SBA-15 catalyst (60%) was prepared by step coating NH3/water vapor-induced internal hydrolysis (VIH) and characterized by X-ray diffraction, N2 adsorption-desorption, and temperature-programmed reduction (H2-TPR). Its catalytic performance for toluene combustion was also evaluated. The results showed that the VIH process clearly improved the activity of the LaMnOx/SBA-15 catalyst. Using a toluene concentration of 0.86% and a GHSV of 5000 h−1, a 50% toluene conversion was obtained at 205 °C for the LaMnOx/SBA-15 sample prepared by the VIH process. This temperature was 105 °C lower than that for the sample prepared by conventional impregnation. N2 adsorption-desorption and H2-TPR revealed that the VIH process improved the distribution of the LaMnOx active phase in the pores of SBA-15 and improved its reduction properties. The optimal VIH conditions were a temperature of 60 °C and a reaction time of 40 min.

High Selectivity of Cyclohexane Dehydrogenation for H 2 Evolution Over Cu/SBA-15 Catalyst

The effects of metal particle size on catalytic activities of Cu/SBA-15 with different Cu content were investigated for high selectivity of cyclohexane dehydrogenation. Overall, the smaller Cu nanoparticles exhibit higher hydrogen evolution rate or lower active energy barrier. But, even when the smaller CuO nanoparticles have formed on the catalyst with lower Cu content during the calcination, they would be more prone to sinter after reduction. An appropriate Cu content could lead to form amounts of stable and small Cu nanoparticles after high-temperature treatment with the space limitation by ordered channels of SBA-15.Graphical Abstract

Acid treatment and formation of MnWO4 belts for NH3-SCR performance of MnWOx/TiO2 catalysts

NH3-SCR is an important technology to remove NOx, and non-V based catalysts development is still a hot topic in the field. To improve N2 selectivity, acid treatment was carried out to modify the properties of a MnWOx/TiO2 catalyst. Influences of acid concentration, time and temperature on the catalyst were investigated. The TEM results showed that the acid treatment removed more MnO2 species than Mn2O3 and MnWO4 and disclosed more crystal faces of the active species. The active species even formed hollow structures by Ostwald ripening mechanism, which was then corroded by acid to form the nanobelts on the surface. The working temperature window of the MnWOx/TiO2 catalyst was thereby moved to the high temperature attitude and the N2 selectivity is clearly improved.NH3-SCR is an important technology to remove NOx, and non-V based catalysts development is still a hot topic in the field. To improve N2 selectivity, acid treatment was carried out to modify the properties of a MnWOx/TiO2 catalyst. Influences of acid concentration, time and temperature on the catalyst were investigated. The TEM results showed that the acid treatment removed more MnO2 species than Mn2O3 and MnWO4 and disclosed more crystal faces of the active species. The active species even formed hollow structures by Ostwald ripening mechanism, which was then corroded by acid to form the nanobelts on the surface. The working temperature window of the MnWOx/TiO2 catalyst was thereby moved to the high temperature attitude and the N2 selectivity is clearly improved.

Photo reduction of CO2 to CH4 on g-C3N4: The effect of concentrating light and pretreatment

The behavior of CO2 photoreduction to CH4 on the g−C3N4 catalyst was studied in a concentrating light reactor. The g−C3N4 catalysts before and after pretreatment were characterized by FE−SEM, XRD and photoilluminance. It is found that concentrating light increases the CH4 yield on the g−C3N4 by heightening the incident light intensity, and light pretreatment has an excessive effect on the performance. Pretreated by suitable light intensity, air atmosphere and time, the CH4 yield on the g-C3N4 under concentrating light irradiation reached about 3.39 μmol·g-1·h-1, which is about 16 times of that g−C3N4 reacted at nature incident light without pretreatment. The mechanism of pretreatment is considered to be from the surface oxidation state change of the catalyst either from the oxidation of the catalyst surface or the activation of surface oxygen.The behavior of CO2 photoreduction to CH4 on the g−C3N4 catalyst was studied in a concentrating light reactor. The g−C3N4 catalysts before and after pretreatment were characterized by FE−SEM, XRD and photoilluminance. It is found that concentrating light increases the CH4 yield on the g−C3N4 by heightening the incident light intensity, and light pretreatment has an excessive effect on the performance. Pretreated by suitable light intensity, air atmosphere and time, the CH4 yield on the g-C3N4 under concentrating light irradiation reached about 3.39 μmol·g-1·h-1, which is about 16 times of that g−C3N4 reacted at nature incident light without pretreatment. The mechanism of pretreatment is considered to be from the surface oxidation state change of the catalyst either from the oxidation of the catalyst surface or the activation of surface oxygen.

Mayenite supported perovskite monoliths for catalytic combustion of methyl methacrylate

To improve their thermal stability, La0.8Sr0.2MnO3 cordierite monoliths are washcoated with mayenite, which is a novel Al-based material with the crystal structure of 12MO·7Al2O3 (M = Ca, Sr). The monoliths are characterized by means of nitrogen adsorption/desorption, scanning electron microscopy, and X-ray diffraction. Catalytic performances of the monoliths are tested for methyl methacrylate combustion. The results show that mayenite obviously improves both the physicchemical properties and the catalytic performance of the monoliths. Because mayenite improves the dispersity of La0.8Sr0.2MnO3 and also prevents the interaction between La0.8Sr0.2MnO3 and cordierite or γ-Al2O3, both crystal structure and surface morphology of La0.8Sr0.2MnO3 phase can thereby be stable on the mayenite surface even at high temperature up to 1050 °C. Under the given reaction conditions, La0.8Sr0.2MnO3 monolith washcoated with 12SrO·7Al2O3 shows the best catalytic activity for methyl methacrylate combustion among all the tested monoliths.

Facile preparation of Fe-Y catalyst under water-free conditions for selective catalytic reduction of NO x by ammonia

A series of Fe-Y zeolite catalysts with different Fe loading were prepared by ferrocene sublimation under solvent and water-free conditions. The dispersion, structure and morphology of the iron species on the Fe-Y catalysts were characterized by XRD, TEM and UV-Vis. The catalytic activities of Fe-Y samples were measured in selective catalytic reduction of NO with ammonia (NH3-SCR). The results showed that the iron species on the HY zeolite support were mainly made up of isolated Fe3+ ions, FexOy oligomers and a little amount of < 3 nm spherical Fe2O3 particles. Isolated Fe3+ ions are predominating among all the Fe-Y catalysts. The sum of isolated Fe3+ ions and FexOy oligomers took up more than 90% percent of total iron species on the Fe-Y till 10.0 wt% loading of Fe.