The reduction features of Co_ 3 O_ 4 and Pt/Co_ 3 O_ 4 were studied by electrical conductivity in this paper. Combined with the TPR results, it is concluded that the presence of noble metal Pt could significantly decr...The reduction features of Co_ 3 O_ 4 and Pt/Co_ 3 O_ 4 were studied by electrical conductivity in this paper. Combined with the TPR results, it is concluded that the presence of noble metal Pt could significantly decrease the reduction temperature of Co_ 3 O_ 4 . In addition, the electrical conductance ratios of Co_ 3 O_ 4 and Pt/Co_ 3 O_ 4 under different atmospheres, which are in a consecutively changing sequence of hydrogen, oxygen and syngas, were also investigated. It is found that the cobalt oxides resulted from the oxidation of Co metal under oxygen atmosphere can be re-reduced by the syngas in the presence of Pt noble metal. Because the electrical conductance study was conducted at 493 K, which is close to the typical reaction temperature of Fischer-Tropsch synthesis with cobalt based catalysts. It is reasonably speculated that the presence of Pt is beneficial to inhibiting the oxidation of cobalt metal during the Fischer-Tropsch synthesis, and thus eliminating the deactivation of cobalt catalyst.展开更多
Closed-form and asymptotic solutions are derived for the steady, fully-developed hydromagnetic free and forced convection flow in a rotating horizontal parallel-plate channel under the action of an inclined magnetic f...Closed-form and asymptotic solutions are derived for the steady, fully-developed hydromagnetic free and forced convection flow in a rotating horizontal parallel-plate channel under the action of an inclined magnetic field and constant pressure gradient along the longitudinal axis of the channel. The magnetic field is strong enough to generate Hall current effects and the magnetic Reynolds number of sufficient magnitude that induced magnetic field effects are also present. Secondary flow is present owing to the Hall current effect. The channel plates are also taken to be electrically-conducting. The conservation equations are formulated in an (x, y, z) coordinate system and non-dimensionalized using appropriate transformations. The resulting non-dimensional coupled ordinary differential equations for primary and secondary velocity components and primary and secondary induced magnetic field components and transformed boundary conditions are shown to be controlled by the dimensionless pressure gradient parameter (px), Hartmann number (M2), Grashof number (G), Hall current parameter (m), rotational parameter (K2), magnetic field inclination (Θ), and the electrical conductance ratios of the upper (⏱) and lower (⏲) plates. Solutions are derived using the method of complex variables. Asymptotic solutions are also presented for very high rotation parameter and Hartmann number of order equal to unity, for which Ekman-Hartmann boundary layers are identified at the plates. A parametric study of the evolution of velocity and induced magnetic field distributions is undertaken. It is shown that generally increasing Hall current effect (m) serves to accentuate the secondary (cross) flow but oppose the primary flow. An increase in rotational parameter (K2) is also found to counteract primary flow intensity. An elevation in the Grashof number i.e. free convection parameter (G) is shown to aid the secondary induced magnetic field component (Hz);however there is a decrease in magnitudes of the primary induced magnetic展开更多
基金supported by the National Natural Science Foundation of China(11504041)the Fundamental Research Funds for the Central Universities of China(DUT16LAB01,DUT17LAB19)the Supercomputing Center of Dalian University of Technology,China~~
文摘The reduction features of Co_ 3 O_ 4 and Pt/Co_ 3 O_ 4 were studied by electrical conductivity in this paper. Combined with the TPR results, it is concluded that the presence of noble metal Pt could significantly decrease the reduction temperature of Co_ 3 O_ 4 . In addition, the electrical conductance ratios of Co_ 3 O_ 4 and Pt/Co_ 3 O_ 4 under different atmospheres, which are in a consecutively changing sequence of hydrogen, oxygen and syngas, were also investigated. It is found that the cobalt oxides resulted from the oxidation of Co metal under oxygen atmosphere can be re-reduced by the syngas in the presence of Pt noble metal. Because the electrical conductance study was conducted at 493 K, which is close to the typical reaction temperature of Fischer-Tropsch synthesis with cobalt based catalysts. It is reasonably speculated that the presence of Pt is beneficial to inhibiting the oxidation of cobalt metal during the Fischer-Tropsch synthesis, and thus eliminating the deactivation of cobalt catalyst.
文摘Closed-form and asymptotic solutions are derived for the steady, fully-developed hydromagnetic free and forced convection flow in a rotating horizontal parallel-plate channel under the action of an inclined magnetic field and constant pressure gradient along the longitudinal axis of the channel. The magnetic field is strong enough to generate Hall current effects and the magnetic Reynolds number of sufficient magnitude that induced magnetic field effects are also present. Secondary flow is present owing to the Hall current effect. The channel plates are also taken to be electrically-conducting. The conservation equations are formulated in an (x, y, z) coordinate system and non-dimensionalized using appropriate transformations. The resulting non-dimensional coupled ordinary differential equations for primary and secondary velocity components and primary and secondary induced magnetic field components and transformed boundary conditions are shown to be controlled by the dimensionless pressure gradient parameter (px), Hartmann number (M2), Grashof number (G), Hall current parameter (m), rotational parameter (K2), magnetic field inclination (Θ), and the electrical conductance ratios of the upper (⏱) and lower (⏲) plates. Solutions are derived using the method of complex variables. Asymptotic solutions are also presented for very high rotation parameter and Hartmann number of order equal to unity, for which Ekman-Hartmann boundary layers are identified at the plates. A parametric study of the evolution of velocity and induced magnetic field distributions is undertaken. It is shown that generally increasing Hall current effect (m) serves to accentuate the secondary (cross) flow but oppose the primary flow. An increase in rotational parameter (K2) is also found to counteract primary flow intensity. An elevation in the Grashof number i.e. free convection parameter (G) is shown to aid the secondary induced magnetic field component (Hz);however there is a decrease in magnitudes of the primary induced magnetic
