In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduct...In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduction of WO_(3)-Co_(3)O_(4)to WO_(2)-Co and then deep reduction carbonization to WC-Co powder has been proposed.This study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO_(3)-Co_(3)O_(4)under a mixed atmosphere of H_(2)-C_(2)H_(4)-Ar at 600℃and establishes the kinetic equations of pre-reduction and carbon evolution.The results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO_(3) to WO_(2).High carbon content can be generated by the deposition of C_(2)H_(4),and it hinders the diffusion of the reducing gas;WO_(3)still cannot be completely reduced to WO_(2)as the partial pressure of C_(2)H_(4) increases to 60%.For the carbon evolution of C_(2)H_(4),the carbon amount is positively related to the H_(2)partial pressure,but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%.Based on the reduction rate curves of WO_(3) and carbon evolution rate curves of C_(2)H_(4),the rate equations of pre-reduction and carbon evolution of WO_(3)-Co_(3)O_(4)system at 600℃are established.The pre-reduction reaction belongs to the first-order reaction,and its equation is expressed as follows:r=-(dw_(WO_(3)))/dt=(9±0.15)×10^(-2)×P_(H_(2))^(0.44)P_(C_(2)H_(4))&(0.57)The carbon deposition rate equation of C_(2)H_(4) can be expressed as follows:r=-(dc_C)/dt=r_f-r_b≌7.35×10^(-2)×P_(C_(2)H_(4))^(0.31)展开更多
In this study,Mn-Na_(2)WO_(4)/γ-Al_(2)O_(3) catalysts with varying ratios of Mn/W were prepared using the dry impregnation method.These catalysts were then tested for their suitability in the oxidative coupling of me...In this study,Mn-Na_(2)WO_(4)/γ-Al_(2)O_(3) catalysts with varying ratios of Mn/W were prepared using the dry impregnation method.These catalysts were then tested for their suitability in the oxidative coupling of methane reaction.The X-ray photoelectron results revealed the presence of the tetrahedral WO_(4)^(2–)phase in all prepared catalysts.It is believed that the presence of this phase is associated with high catalyst activity,indicating the potential of the catalysts for the desired reaction.The activity results show that the catalyst with a high Mn/W ratio exhibited higher activity at 800℃,whereas the catalyst with a low Mn/W ratio showed greater activity at 850℃.This suggests that the Mn/W ratio influences the reaction temperature at which the catalyst is most active.Furthermore,the X-ray diffraction results of the treated catalysts revealed that the catalyst with a high Mn/W ratio exhibited more MnAl_(2)O_(4) at 800℃,whereas the catalyst with a low Mn/W ratio contained more MnWO_(4) at 850℃.The results suggest that the presence of MnAl_(2)O_(4) sites may promote a more facile Mn^(2+)↔Mn^(3+)cycle at lower temperatures than the MnWO_(4) site,potentially contributing to the enhanced catalyst activity in the oxidative coupling of methane reaction at 800℃.展开更多
A new vertically aligned nanocomposite(VAN)structure based on two-dimensional(2D)layered oxides has been designed and self-assembled on both LaAlO_(3)(001)and SrTiO3(001)substrates.The new VAN structure consists of ep...A new vertically aligned nanocomposite(VAN)structure based on two-dimensional(2D)layered oxides has been designed and self-assembled on both LaAlO_(3)(001)and SrTiO3(001)substrates.The new VAN structure consists of epitaxially grown Co_(3)O_(4) nanopillars embedded in the Bi_(2)WO_(6) matrix with a unique 2D layered structure,as evidenced by the microstructural analysis.Physical property measurements show that the new Bi_(2)WO_(6)-Co_(3)O_(4) VAN structure exhibits strong ferromagnetic and piezoelectric response at room temperature as well as anisotropic permittivity response.This work demonstrates a new approach in processing multifunctional VANs structure based on the layered oxide systems towards future nonlinear optics,ferromagnets,and multiferroics.展开更多
基金the National Natural Science Foundation of China(22078326,21878305,21908227)。
文摘In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduction of WO_(3)-Co_(3)O_(4)to WO_(2)-Co and then deep reduction carbonization to WC-Co powder has been proposed.This study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO_(3)-Co_(3)O_(4)under a mixed atmosphere of H_(2)-C_(2)H_(4)-Ar at 600℃and establishes the kinetic equations of pre-reduction and carbon evolution.The results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO_(3) to WO_(2).High carbon content can be generated by the deposition of C_(2)H_(4),and it hinders the diffusion of the reducing gas;WO_(3)still cannot be completely reduced to WO_(2)as the partial pressure of C_(2)H_(4) increases to 60%.For the carbon evolution of C_(2)H_(4),the carbon amount is positively related to the H_(2)partial pressure,but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%.Based on the reduction rate curves of WO_(3) and carbon evolution rate curves of C_(2)H_(4),the rate equations of pre-reduction and carbon evolution of WO_(3)-Co_(3)O_(4)system at 600℃are established.The pre-reduction reaction belongs to the first-order reaction,and its equation is expressed as follows:r=-(dw_(WO_(3)))/dt=(9±0.15)×10^(-2)×P_(H_(2))^(0.44)P_(C_(2)H_(4))&(0.57)The carbon deposition rate equation of C_(2)H_(4) can be expressed as follows:r=-(dc_C)/dt=r_f-r_b≌7.35×10^(-2)×P_(C_(2)H_(4))^(0.31)
基金support of the Ferdowsi University of Mashhad Research Council,Mashhad,Iran(Grant No.68841)and(OCM project No.23346).
文摘In this study,Mn-Na_(2)WO_(4)/γ-Al_(2)O_(3) catalysts with varying ratios of Mn/W were prepared using the dry impregnation method.These catalysts were then tested for their suitability in the oxidative coupling of methane reaction.The X-ray photoelectron results revealed the presence of the tetrahedral WO_(4)^(2–)phase in all prepared catalysts.It is believed that the presence of this phase is associated with high catalyst activity,indicating the potential of the catalysts for the desired reaction.The activity results show that the catalyst with a high Mn/W ratio exhibited higher activity at 800℃,whereas the catalyst with a low Mn/W ratio showed greater activity at 850℃.This suggests that the Mn/W ratio influences the reaction temperature at which the catalyst is most active.Furthermore,the X-ray diffraction results of the treated catalysts revealed that the catalyst with a high Mn/W ratio exhibited more MnAl_(2)O_(4) at 800℃,whereas the catalyst with a low Mn/W ratio contained more MnWO_(4) at 850℃.The results suggest that the presence of MnAl_(2)O_(4) sites may promote a more facile Mn^(2+)↔Mn^(3+)cycle at lower temperatures than the MnWO_(4) site,potentially contributing to the enhanced catalyst activity in the oxidative coupling of methane reaction at 800℃.
基金This work is supported by the U.S.Office of Naval Research(ONR,N00014-20-1-2600)The high-resolution TEM/STEM characterization at Purdue University is supported by the U.S.National Science Foundation(Nos.DMR-1565822 and DMR-2016453)。
文摘A new vertically aligned nanocomposite(VAN)structure based on two-dimensional(2D)layered oxides has been designed and self-assembled on both LaAlO_(3)(001)and SrTiO3(001)substrates.The new VAN structure consists of epitaxially grown Co_(3)O_(4) nanopillars embedded in the Bi_(2)WO_(6) matrix with a unique 2D layered structure,as evidenced by the microstructural analysis.Physical property measurements show that the new Bi_(2)WO_(6)-Co_(3)O_(4) VAN structure exhibits strong ferromagnetic and piezoelectric response at room temperature as well as anisotropic permittivity response.This work demonstrates a new approach in processing multifunctional VANs structure based on the layered oxide systems towards future nonlinear optics,ferromagnets,and multiferroics.
