Thermally Activated Cr<SUB>2</SUB>O<SUB>3+<I>x</I></SUB> for Elimination of Volatile Organic Compounds

Abstract

We have previously shown that oxide semiconductors (for example, TiO 2 , NiO, etc.) exhibit significant catalytic effects when heated at about 350-500C. 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 Cr 2 O 3þx (0 < x < 1) in an attempt to lower the operation temperature of VOC decomposition. We present here how the low-temperature operation proceeds with Cr 2 O 3þx and also elucidate why Cr 2 O 3þx is colored green, on the basis of the temperature dependences of electrical conductivity and Seebeck potential of Cr 2 O 3þx . The green color of Cr 2 O 3þx is found to arise from Cr vacancies in Cr 2 O 3þx , 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.

VOC Decomposition System Based upon Heater-Integrated Catalyst Units Using NiO or Cr<SUB>2</SUB>O<SUB>3</SUB>

“…1) In view of the present situation, we started our investigation on complete removal of VOC and organic wastes by means of thermally excited holes in oxide semiconductors such as TiO 2 , [4][5][6][7][8][9][10][11][12][13] NiO, 14) Cr 2 O 3 15,16) and -Fe 2 O 3 17) at about 350-500 C. The use of thermally generated holes for removal of VOC and organic wastes is an entirely new technology initiated by us in 2001.…”

Instantaneous and Complete Decomposition of Formaldehyde by Thermally Activated Oxide Semiconductors

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Our system for complete elimination of volatile organic compounds (VOCs) has the advantage of being efficient, compact and inexpensive. Our technology has been initiated by an accidental finding that oxide semiconductors such as TiO 2 exhibit no catalytic activity at room temperature, but the activity is greatly enhanced when heated at above 350-500 C. [5][6][7] The present technology uses a large number of highly oxidative holes generated by thermal excitation of semiconductors for decomposition of plastics as well as VOCs in an instant.…”

“…Our technology has been initiated by an accidental finding that oxide semiconductors such as TiO 2 exhibit no catalytic activity at room temperature, but the activity is greatly enhanced when heated at above 350-500 C. [5][6][7] The present technology uses a large number of highly oxidative holes generated by thermal excitation of semiconductors for decomposition of plastics as well as VOCs in an instant. Up to now, we have shown very successful results for complete decomposition of plastics, 6,7) volatile organic compounds, 8,11,[13][14][15]17,18,20) diesel exhausts, 8) tobacco smokes, recovery of glass fibers from fiber reinforced plastics, 21) side by side with the system development based on the fundamental elucidation of the decomposition mechanism.…”

Recovery of Glass Fibers from Fiber Reinforced Plastics

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] This novel technology developed by us has mainly been used for complete decomposition of thermoplastic or thermosetting polymers, as well as volatile organic compounds (VOCs). However, this technology has never been tested so far for the recovery of glass fibers from FRPs.…”