Thermally Activated Cr₂O_3+x for Elimination of Volatile Organic Compounds

Abstract

We have previously shown that oxide semiconductors (for example, TiO₂, NiO, etc.) exhibit significant catalytic effects when heated at about 350–500°C. This is due to the formation of a vast number of highly oxidative holes at high temperatures. Then, we applied the present finding for complete removal of volatile organic compounds (VOCs). In the present investigation, we focused on Cr₂O_3+x (0<x<1) in an attempt to lower the operation temperature of VOC decomposition. We present here how the low-temperature operation proceeds with Cr₂O_3+x and also elucidate why Cr₂O_3+x is colored green, on the basis of the temperature dependences of electrical conductivity and Seebeck potential of Cr₂O_3+x. The green color of Cr₂O_3+x is found to arise from Cr vacancies in Cr₂O_3+x, and the vacancies are responsible for the formation of a narrow conduction band or a deep acceptor level, resulting in the low-temperature operation of VOC decomposition.