还原温度对Mo基催化剂物相及其加氢脱氧性能的影响

以碳纳米管(CNTs)为载体,通过控制催化剂合成的还原温度制备了一系列负载型Mo基催化剂。采用XRD、TEM、N₂物理吸附、XPS以及NH₃/H₂-TPD等技术对催化剂进行了表征,并研究了Mo基催化剂对硬脂酸催化加氢脱氧性能的影响。结果表明:随着还原温度的升高,催化剂表面的Mo物种逐渐被还原,还原过程为:MoO₃→MoO₂→Mo→Mo₂C。还原温度为450℃和550℃时,催化剂的活性相为MoO₂;还原温度为600℃时,催化剂的活性相为MoO₂/Mo/β-Mo₂C的混合相;还原温度为650℃和700℃时,催化剂的活性相全部转化为β-Mo₂C。与活性相MoO₂催化剂相比,β-Mo₂C催化剂具有更高的加氢脱氧活性。此外,还原温度为600℃的MoO₂/Mo/β-Mo₂C混合相催化剂因具有较大的比表面积、较多的酸中心数量和较强的H₂吸附能力,使得该催化剂在硬脂酸加氢脱氧反应中表现出最优越的催化活性。

Effect of reduction temperature on Mo-based catalyst phase and its activity in hydrodeoxygenation reaction

A series of Mo-based catalysts supported over CNTs were successfully prepared by controlling the reduction temperature during the catalyst synthesis. The properties of the obtained catalysts were systematically characterized by XRD, TEM, N₂ adsorption, XPS and NH₃/H₂-TPD techniques, and the catalytic reactivity for the hydrodeoxygenation of stearic acid was evaluated. The results showed that Mo species on the surface of catalysts were reduced with the increase of reduction temperature, and the reduction process was as followed: MoO₃→MoO₂→Mo→Mo₂C. The active phase was MoO₂when reduction temperature was below 550℃. Further elevating the reduction temperature to 600℃, we found a mixed phase of MoO₂/Mo/β-Mo₂C existed. β-Mo₂C was the main active phase when reduction temperature was over 650℃, and it exhibited higher activity of hydrodeoxygenation than the active phase of MoO₂. In addition, the MoO₂/Mo/β-Mo₂C mixed phase catalyst at 600℃ showed the highest catalytic reactivity in hydrodeoxygenation of stearic acid due to its large specific surface area, more acid sites and stronger H₂ adsorption ability.