Cr-WO_(3)超细纳米线用于苯乙烯选择性氧化制苯甲醛

Selective oxidation of styrene to benzaldehyde with Cr-WO_(3)ultrafine nanowires

本工作在水热法制备WO_(3)过程中直接引入Cr3+作为改性剂,其在非(001)晶面的选择性吸附,实现了WO_(3)形貌从纳米棒到[001]取向超细纳米线(UNWs)的转变,最终所得Cr-WO_(3)UNWs催化剂的比表面积可达297 m2/g。此外,Cr3+的晶格掺杂和减缓结晶作用有效增加了WO_(3)表面氧空位(L酸位点)浓度。在苯乙烯选择性氧化制苯甲醛反应中,最佳条件下(70℃、r(nH_(2)O_(2)/n苯乙烯)=2.0、6 h、m=30 mg),Cr-WO_(3)UNWs分别将苯乙烯转化率和苯甲醛选择性从单一WO_(3)纳米棒的19.0%和49.6%提升到72.0%和84.6%,其催化性能的提升归结于以下两点:第一,超大比表面积可提供充足的反应活性位点;第二,L酸位点可将H_(2)O_(2)活化为W-OOH活性物种,L酸位点浓度的增加有利于更多活性物种的产生。

The oxidation of styrene to benzaldehyde has advantages of mild conditions and no chlorine impurities in the product,and the design of highly active catalyst is the core.As a solid acid catalyst,WO_(3)has excellent performance in thermal oxidation reaction,but its activity is limited by small specific surface area and high B acid content.In this work,the Cr3+cation was introduced as a modifier during the preparation of WO_(3).The adsorption of Cr3+cations on non-(001)crystal plane realized the transformation of WO_(3)from nanorods to ultrafine nanowires(UNWs),and the specific surface area of obtained Cr-WO_(3)UNWs increased to 297 m2/g.In addition,Cr3+cation could dope into the lattice of WO_(3)and slow down its crystallization,both of which effectively enriched the surface oxygen vacancies(L acid sites)of WO_(3).In the reaction of selective oxidation of styrene to benzaldehyde,Cr-WO_(3)UNWs effectively increased the conversion of styrene and the selectivity of benzaldehyde from 19.0%and 49.6%of pure WO_(3)nanorod to 72.0%and 84.6%respectively under the optimized condition of 70℃,r(nH_(2)O_(2)/nstyrene)=2.0,6 h and m=30 mg.The improvement of catalytic performance can be attributed to the following two reasons:(1)the large specific surface area can provide sufficient active site for reaction;(2)the L acid site can activate H_(2)O_(2)into active W-OOH,and an increase in the concentration of L acid site is beneficial for the production of more active species.