高效镍基氨分解催化体系中载体作用的研究

INVESTIGATION ON THE ROLE OF SUPPORT IN THE HIGH-PERFORMANCE NICKEL-BASED CATALYTIC SYSTEM FOR AMMONIA DECOMPOSITION

选用无水乙醇为溶剂,采用浸渍法制备了纳米结构的Ni/Al2O3、Ni/La-Al2O3、Ni/MgO和Ni/TiO2催化剂,并在常压连续微反装置上分别对其氨分解反应活性进行评价。结果表明,4种负载型镍催化剂的活性顺序为Ni/La-Al2O3>Ni/Al2O3 Ni/TiO2>Ni/MgO。当反应温度为600℃时,Ni/La-Al2O3催化剂上H2的生成速率可达873 mmol/(g(Ni).min。对不同Ni负载量的Ni/La-Al2O3催化剂进行XRD分析表明,即使Ni负载量高达14%(质量分数),活性组分在载体上仍然呈高度分散状态。载体对镍基氨分解催化剂的表观活化能具有显著影响。其中,当Ni负载量为3%(质量分数)时,Ni/Al2O3、Ni/La-Al2O3、Ni/MgO和Ni/TiO2催化剂的反应活化能分别为108、119、102和120 kJ/mol。当载体相同时,催化剂氨分解活性主要受反应活化能的影响,反应活化能越高,氨分解活性越低。

The Ni/Al2O3, Ni/La-Al2O3, Ni/MgO and Ni/TiO2 catalysts were synthesized by the impregnation method with the anhydrous ethanol as the solvent. Their catalytic activities towards the NH3 decomposition reaction were evaluated in a continuous-flow reactor under the atmospheric pressure. It is found that the activities of Ni-based catalysts decreased as the order of Ni/La-Al2O3 〉 Ni/Al2O3 〉〉 Ni/TiO2 〉 Ni/MgO. A production rate of H2 as high as 873 mmol/（g（Ni） ·min） could be achieved at 600℃. The crystal phases of the Ni/La-Al2O3 catalysts with different Ni content were analyzed by the XRD technique, which revealed that the active phase remained at a high dispersion state even though the Ni（mass fraction） was as high as 14%. Support significantly influenced the apparent activation energies of Ni-based catalysts for NH3 decomposition. While the Ni loading was 3% （mass fraction）, the obtained activation energies over Ni/Al2O3, Ni/La-Al2O3, Ni/MgO and Ni/TiO2 catalysts were 108, 119, 102 and 120 kJ/mol, respectively. If the same support was used, the catalytic activity for NH3 decomposition was mainly influenced by apparent activation energy, i.e. the higher the activation energy, the lower the production rate.