噻吩脱硫过程中钒氧化物晶格氧的作用

Effect of Lattice Oxygen of Vanadium Oxides on Thiophene Desulfurization

以γ-Al2O3、VO2和V2O5为催化剂,在连续固定床微反装置上、500℃下,考察了噻吩在常压下的脱硫反应过程,并进行了噻吩原位吸附红外光谱、XPS光电子能谱、XRD等表征。结果表明,在催化裂化反应条件下,采用具有单纯L酸中心的催化剂时,噻吩脱硫反应的转化率很低;采用具有单纯氧化-还原中心的催化剂时,噻吩可被氧化成CO、CO2及SO2,但转化率也较低;采用既具有酸中心又具有氧化-还原中心的V2O5时,由于酸中心和氧化-还原中心的协同作用,噻吩脱硫反应的转化率最高,H2S和SO2的产率也最高。催化裂化反应条件下,噻吩可以被钒氧化物的晶格氧氧化,同时V2O5与VO2失去部分晶格氧被还原为V2O3等低价态产物;由于V2O5比VO2活泼晶格氧数目多,较易被还原,因此噻吩脱硫反应的SO2产率更高。V2O5表面存在的L酸中心Vn+-O-V为噻吩的初始吸附中心,L酸中心与临近的V=O双键的作用促进了噻吩的氧化。

The desulfurization reactions of thiophene over γ-Al2O3, VO2 and V2Os catalysts were carried out on a continuous fixed bed reactor at 500℃ under atmospheric pressure. The vanadium oxide catalysts were characterized by IR, XPS and XRD. The results showed that under catalytic cracking conditions, the conversion rate of thiophene over the catalyst with single Lewis acid sites was very low, while thiophene could be converted to CO, CO2 and SO2 over the catalyst with single redox sites, and the conversion rate was low as well. V205 catalyst possessed both acid site and active lattice oxygen, which would cooperate with each other during the desulfurization reactions of thiophene to generate high conversion of thiophene and high yields of H2S and SO2. Thiophene could be oxidized by the lattice oxygen of vanadium oxides under FCC condition and the vanadium oxides could be reduced to lower valence oxides, e. g. V2Oa. V205 possessed more active lattice oxygen compared with VO2, thus it exhibited the highest yield of SO2. The Lewis acid sites Vn＋ -O-V of V2O5 could be the initial adsorption site for thiophene, the synergetic effect of the said acid site and the adjacent V= O double bond might promote the oxidation of thiophene.