生物乙醇重整制氢用ZSM-5催化剂的载体碱改性研究

Alkali modification of ZSM-5 supports for Hydrogen production by ethanol reforming

为获得酸性较低且结构较为完整的ZSM-5分子筛,采用KOH溶液对ZSM-5分子筛进行碱改性,得到K-ZSM-5分子筛,并通过XRD,SEM,NH3-TPD和CO2-TPD等手段,研究了KOH浓度及改性时间对样品的物相、结晶度和酸碱性等特性的影响。结果表明:在改性时间为12 h的条件下,当KOH浓度为0.1 mol/L时,原有H-ZSM-5的强酸位被削除,弱酸位大幅减弱,但继续提高KOH浓度不能进一步削弱样品的弱酸位;在KOH浓度为0.5 mol/L的条件下,当改性时间为4 h时,样品的结晶度和碱量均较高;在改性时间为4 h的条件下,不同KOH浓度的样品均没有SiO2生成,样品的碱量随着KOH浓度的提高先上升后下降。

ZSM-5 supports for hydrogen production by ethanol reforming were mostly H-ZSM-5 zeolites, which would promote ethanol dehydration and the formation of carbon accumulation be- cause of strong acidity, therefore reduce hydrogen selectivity. In order to obtain ZSM-5 zeolite with weaker acidity, K-ZSM-5 zeolite samples were got by alkali treatment of ZSM-5 using KOH solu- tion. Influences of KOH concentration and treating time on samples structure, crystallinity, acidity and basicity were studied by the methods of XRD, SEM, NH3-TPD and CO2-TPD. Results showed that： the strong acidity sites of H-ZSM-5 zeolite were perished and the weak acidity sites were greatly reduced by 0.1 mol/L KOH solution for 12 h, but the weak acidity sites was not further weaken by KOH concentration. For 0.5 mol/L KOH solution, however, when treating time was 4 h, samples could obtain higher crystallinity and larger amount of alkali. Under the treating time for 4 h, SiO2 was not detected in samples treated by KOH solutions with different concentration, and the amount of alkali was firstly increased and then decreased with the increasing of KOH concentra- tion.