In this work,we develop energy stable numerical methods to simulate electromagnetic waves propagating in optical media where the media responses include the linear Lorentz dispersion,the instantaneous nonlinear cubic ...In this work,we develop energy stable numerical methods to simulate electromagnetic waves propagating in optical media where the media responses include the linear Lorentz dispersion,the instantaneous nonlinear cubic Kerr response,and the nonlinear delayed Raman molecular vibrational response.Unlike the first-order PDE-ODE governing equations considered previously in Bokil et al.(J Comput Phys 350:420–452,2017)and Lyu et al.(J Sci Comput 89:1–42,2021),a model of mixed-order form is adopted here that consists of the first-order PDE part for Maxwell’s equations coupled with the second-order ODE part(i.e.,the auxiliary differential equations)modeling the linear and nonlinear dispersion in the material.The main contribution is a new numerical strategy to treat the Kerr and Raman nonlinearities to achieve provable energy stability property within a second-order temporal discretization.A nodal discontinuous Galerkin(DG)method is further applied in space for efficiently handling nonlinear terms at the algebraic level,while preserving the energy stability and achieving high-order accuracy.Indeed with d_(E)as the number of the components of the electric field,only a d_(E)×d_(E)nonlinear algebraic system needs to be solved at each interpolation node,and more importantly,all these small nonlinear systems are completely decoupled over one time step,rendering very high parallel efficiency.We evaluate the proposed schemes by comparing them with the methods in Bokil et al.(2017)and Lyu et al.(2021)(implemented in nodal form)regarding the accuracy,computational efficiency,and energy stability,by a parallel scalability study,and also through the simulations of the soliton-like wave propagation in one dimension,as well as the spatial-soliton propagation and two-beam interactions modeled by the two-dimensional transverse electric(TE)mode of the equations.展开更多
A series of supported molybdenum phosphide catalysts were prepared by impregnation method. XRD, TG-DTG, XPS and BET were used to study the phase, compositions and surface areas of the prepared catalysts. A model react...A series of supported molybdenum phosphide catalysts were prepared by impregnation method. XRD, TG-DTG, XPS and BET were used to study the phase, compositions and surface areas of the prepared catalysts. A model reactant containing thiophene, pyridine and cyclohexene was used for the measurements of catalytic activities. The effect of reduction temperature on catalytic activities was investigated. The analysis results by XRD and BET are very different when the reduction temperature is changed from 400 to 900 ℃. MoP/γ-Al2O3 catalysts and CoMoP/γ-Al2O3 catalysts prepared at the reduction temperature of 500 ℃ are the most active ones.展开更多
Using cheap n-butylamine as template, ZSM-5 zeolites have been successfully synthesized and coated on mon- olithic interconnected macroporous Al2O3 by the secondary growth method. The use of cheap n-butylamine could s...Using cheap n-butylamine as template, ZSM-5 zeolites have been successfully synthesized and coated on mon- olithic interconnected macroporous Al2O3 by the secondary growth method. The use of cheap n-butylamine could significantly reduce the synthesis cost. Hierarchical monolithic ZSM-5 zeolites were prepared from synthetic mix- tures with different H2O/Na2O or SiO2/Al2O3 ratio. The synthesized samples were characterized by scanning elec- tron microscopy （SEM）, X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FT-IR） and N2 ad- sorption-desorption. The results show that the hierarchical monolithic zeolites were obtained with cheap n-butylamine template as template. During the hydrothermal reaction process, the morphology of the microme- ter-sized support was well maintained. The irregular crystals were formed in a wide range of the H2O/Na2O or SiO2/Al2O3 ratio of synthetic mixtures and coated on monolithic Al2O3. The relative crystallinity of the zeolites was highest at H2O/Na2O=250 or SiO2/Al2O3= 160. This type of composites exhibited hierarchical porous structures and relatively high specific surface areas.展开更多
Rational design and building of high efficiency,secure and inexpensive electrocatalyst is a pressing demand and performance to promote sustainable improvement of hydrogen energy.The bifunctional electrocatalysts for o...Rational design and building of high efficiency,secure and inexpensive electrocatalyst is a pressing demand and performance to promote sustainable improvement of hydrogen energy.The bifunctional electrocatalysts for oxygen evolution reaction(OER)and hydrogen evolution response(HER)with high catalytic performance and steadiness in the equal electrolyte are extra treasured and meaningful.Herein,a unique three-dimensional(3D)structure electrocatalyst for NiCo_(2)S_(4)growing on the flower-like NiFeP was designed and synthesized in this study.The results show that the flower-like NiCo_(2)S_(4)/NiFeP/NF composite electrocatalyst has large specific surface area,appropriate electrical conductivity,and greater lively websites uncovered in the three-dimensional structure,and affords extraordinary electrocatalytic overall performance for the ordinary water splitting.In alkaline solution,the OER and HER overpotentials of NiCo_(2)S_(4)/NiFeP/NF only need 293 mV and 205 mV overpotential to provide the current densities of 100 mA/cm^(2)and 50 mA/cm^(2),respectively.This high electrocatalytic activity exceeds the catalytic activity of most nickel-iron based electrocatalysts for OER and HER process.Accordingly,the optimized NiCo_(2)S_(4)/NiFeP/NF sample has higher stability(24 h)at 1.560 and 10 mA/cm^(2),which extensively speeds up the overall water splitting process.In view of the above performance,this work offers a fine approach for the further improvement of low fee and excessive effectivity electrocatalyst.展开更多
Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors(supported phospho-tungstate catalysts)in H2 and characterized by X-ray diffraction(XRD),BET,temperature-prog...Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors(supported phospho-tungstate catalysts)in H2 and characterized by X-ray diffraction(XRD),BET,temperature-programmed desorption of ammonia(NH3-TPD)and X-ray photoelectron spectroscopy(XPS).The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis(TG-DTA)and the suitable phosphiding temperatures were defined.The hydrodesulfurization(HDS)and hydrodenitrogenation(HDN)activities of the catalysts were tested by using thiophene,pyridine,dibenzothiophene,carbazole and diesel oil as the feedstock.The TiO2,c-Al_(2)O_(3) supports and the Ni,Co promoters could remarkably increase and stabilize active W species on the catalyst surface.A suitable amount of Ni(3%–5%),Co(5%–7%)and V(1%–3%)could increase dispersivity of the W species and the BET surface area of the WP/c-Al_(2)O_(3) catalyst.The WP/c-Al_(2)O_(3) catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO2 catalyst has much higher dibenzothiophene(DBT)HDS and pyridine HDN activities.The Ni,Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/c-Al_(2)O_(3) catalyst.The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/c-Al_(2)O_(3) catalyst.In general,a support or promoter in the WP/c-Al_(2)O_(3) catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.展开更多
基金supported by China Postdoctoral Science Foundation grant 2020TQ0344the NSFC grants 11871139 and 12101597the NSF grants DMS-1720116,DMS-2012882,DMS-2011838,DMS-1719942,DMS-1913072.
文摘In this work,we develop energy stable numerical methods to simulate electromagnetic waves propagating in optical media where the media responses include the linear Lorentz dispersion,the instantaneous nonlinear cubic Kerr response,and the nonlinear delayed Raman molecular vibrational response.Unlike the first-order PDE-ODE governing equations considered previously in Bokil et al.(J Comput Phys 350:420–452,2017)and Lyu et al.(J Sci Comput 89:1–42,2021),a model of mixed-order form is adopted here that consists of the first-order PDE part for Maxwell’s equations coupled with the second-order ODE part(i.e.,the auxiliary differential equations)modeling the linear and nonlinear dispersion in the material.The main contribution is a new numerical strategy to treat the Kerr and Raman nonlinearities to achieve provable energy stability property within a second-order temporal discretization.A nodal discontinuous Galerkin(DG)method is further applied in space for efficiently handling nonlinear terms at the algebraic level,while preserving the energy stability and achieving high-order accuracy.Indeed with d_(E)as the number of the components of the electric field,only a d_(E)×d_(E)nonlinear algebraic system needs to be solved at each interpolation node,and more importantly,all these small nonlinear systems are completely decoupled over one time step,rendering very high parallel efficiency.We evaluate the proposed schemes by comparing them with the methods in Bokil et al.(2017)and Lyu et al.(2021)(implemented in nodal form)regarding the accuracy,computational efficiency,and energy stability,by a parallel scalability study,and also through the simulations of the soliton-like wave propagation in one dimension,as well as the spatial-soliton propagation and two-beam interactions modeled by the two-dimensional transverse electric(TE)mode of the equations.
文摘A series of supported molybdenum phosphide catalysts were prepared by impregnation method. XRD, TG-DTG, XPS and BET were used to study the phase, compositions and surface areas of the prepared catalysts. A model reactant containing thiophene, pyridine and cyclohexene was used for the measurements of catalytic activities. The effect of reduction temperature on catalytic activities was investigated. The analysis results by XRD and BET are very different when the reduction temperature is changed from 400 to 900 ℃. MoP/γ-Al2O3 catalysts and CoMoP/γ-Al2O3 catalysts prepared at the reduction temperature of 500 ℃ are the most active ones.
基金This work was supported by tile National Natural Science Foundation of China （Nos. B030301 and A020601） and the State Key Laboratory of Catalytic Materials and Reaction Engineering （RIPP, SINOPEC）.
文摘Using cheap n-butylamine as template, ZSM-5 zeolites have been successfully synthesized and coated on mon- olithic interconnected macroporous Al2O3 by the secondary growth method. The use of cheap n-butylamine could significantly reduce the synthesis cost. Hierarchical monolithic ZSM-5 zeolites were prepared from synthetic mix- tures with different H2O/Na2O or SiO2/Al2O3 ratio. The synthesized samples were characterized by scanning elec- tron microscopy （SEM）, X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FT-IR） and N2 ad- sorption-desorption. The results show that the hierarchical monolithic zeolites were obtained with cheap n-butylamine template as template. During the hydrothermal reaction process, the morphology of the microme- ter-sized support was well maintained. The irregular crystals were formed in a wide range of the H2O/Na2O or SiO2/Al2O3 ratio of synthetic mixtures and coated on monolithic Al2O3. The relative crystallinity of the zeolites was highest at H2O/Na2O=250 or SiO2/Al2O3= 160. This type of composites exhibited hierarchical porous structures and relatively high specific surface areas.
基金financially supported by National Key R&D Program of China (No. 2019YFC1907602)National Natural Science Foundation of China (Nos. 51572295, 21273285 and 21003157)
文摘Rational design and building of high efficiency,secure and inexpensive electrocatalyst is a pressing demand and performance to promote sustainable improvement of hydrogen energy.The bifunctional electrocatalysts for oxygen evolution reaction(OER)and hydrogen evolution response(HER)with high catalytic performance and steadiness in the equal electrolyte are extra treasured and meaningful.Herein,a unique three-dimensional(3D)structure electrocatalyst for NiCo_(2)S_(4)growing on the flower-like NiFeP was designed and synthesized in this study.The results show that the flower-like NiCo_(2)S_(4)/NiFeP/NF composite electrocatalyst has large specific surface area,appropriate electrical conductivity,and greater lively websites uncovered in the three-dimensional structure,and affords extraordinary electrocatalytic overall performance for the ordinary water splitting.In alkaline solution,the OER and HER overpotentials of NiCo_(2)S_(4)/NiFeP/NF only need 293 mV and 205 mV overpotential to provide the current densities of 100 mA/cm^(2)and 50 mA/cm^(2),respectively.This high electrocatalytic activity exceeds the catalytic activity of most nickel-iron based electrocatalysts for OER and HER process.Accordingly,the optimized NiCo_(2)S_(4)/NiFeP/NF sample has higher stability(24 h)at 1.560 and 10 mA/cm^(2),which extensively speeds up the overall water splitting process.In view of the above performance,this work offers a fine approach for the further improvement of low fee and excessive effectivity electrocatalyst.
基金State Key Development Basic Research of China(Grant No.G2000048003)the National Natural Science Foundation of China(Grant No.200273011)China Petrochemical Corporation(X501022).
文摘Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors(supported phospho-tungstate catalysts)in H2 and characterized by X-ray diffraction(XRD),BET,temperature-programmed desorption of ammonia(NH3-TPD)and X-ray photoelectron spectroscopy(XPS).The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis(TG-DTA)and the suitable phosphiding temperatures were defined.The hydrodesulfurization(HDS)and hydrodenitrogenation(HDN)activities of the catalysts were tested by using thiophene,pyridine,dibenzothiophene,carbazole and diesel oil as the feedstock.The TiO2,c-Al_(2)O_(3) supports and the Ni,Co promoters could remarkably increase and stabilize active W species on the catalyst surface.A suitable amount of Ni(3%–5%),Co(5%–7%)and V(1%–3%)could increase dispersivity of the W species and the BET surface area of the WP/c-Al_(2)O_(3) catalyst.The WP/c-Al_(2)O_(3) catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO2 catalyst has much higher dibenzothiophene(DBT)HDS and pyridine HDN activities.The Ni,Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/c-Al_(2)O_(3) catalyst.The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/c-Al_(2)O_(3) catalyst.In general,a support or promoter in the WP/c-Al_(2)O_(3) catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.
