焦化烟气中低温SCR催化剂制备及H_2S影响机制研究

Preparation of Mid-Low Temperature SCR Catalysts Used in Coking Flue Gas and the Mechanism of H_2S Influence

选用纳米二氧化钛粉末P25为载体,采用浸渍法制备一系列的V/Mo-Ti催化剂,考察不同V和Mo含量对中、低温脱硝性能及N_2选择性的影响。结果表明:当温度>250℃时,2V/4Mo-Ti具有最好的脱硝效率和氮气选择性,XRD和BET测试结果表明,V和Mo的负载降低催化剂的比表面积和平均孔径,但未改变催化剂的晶型。对V/Mo-Ti催化剂催化氧化H_2S的性能研究发现,V对H_2S有很强的催化氧化能力,含V催化剂在>150℃时H_2S的转化率达到100%,产物主要以SO_2为主。水和H2S对不同催化剂的影响研究结果表明,与4Mo-Ti和2V-Ti相比,2V/4Mo-Ti催化剂的脱硝效率和对H_2S的耐受性均有明显提升,可在焦化烟气脱硝中取得较好效果。水和H2S对2V/4Mo-Ti催化剂耐久性的影响及其影响机理的研究表明,在烟气中存在4%水和0.01%H2S反应10 h后,脱硝效率降到70%左右;停止通水和H_2S后脱硝活性未完全恢复,说明H_2S对催化剂造成了一定的毒害作用。XPS结果显示,催化剂表面有硫酸氢铵生成,并且V5+的含量从65.5%下降至28.6%。以上两方面的因素导致了催化剂活性的降低,为催化剂的改性提供理论依据。

A series of V/Mo-Ti catalysts were prepared by impregnation method with P25 nano titanium dioxide powder as the carrier. The influence of different vanadium and molybdenum content on the denitration and N2 selectivity properties at lowtemperature was investigated,and results showed that when the temperature was higher than 250 ℃,2V/4Mo-Ti had the best denitration efficiency and N2 selectivity. XRD and BET test results showed that the addition of V and Mo did not change the crystal type of the catalyst, but slightly reduce the specific surface area and average pore diameter of catalyst. The performance of V/Mo-Ti catalyst for the catalytic oxidation of H2S was studied,and results showed that V had a strong ability to the catalytic oxidation of H2 S. H2 S conversion rate reached 100% with V containing catalysts higher than 150 ℃,and the products were mainly composed of SO2. The influence of H2S and water was studied on different catalysts,compared with4Mo-Ti and 2V-Ti,the denitration efficiency and resistance of H2S of 2V/4Mo-Ti catalyst were improved significantly,so it could be used in the coking gas denitration process. The influences of H2S and water on the denitration activity were studied and the mechanism was discussed,when 4% water and 0.01% H2S were introduced into the flue gas,the denitration efficiency dropped to 70% after 10 hours. Stop the water and H2S,the denitration were not fully recovered,so we could speculate H2S had a poisoning effect on the denitration activity of the catalyst. XPS results showed that the ammonium hydrogen sulfate was generated on the catalyst surface,and the content of V5 ＋ decreased from 65.5% to 28.6%. The above-mentioned factors contributed to the deactivation of catalyst,which provide the theoretical basis of catalyst modification.