The role of the supports in catalytic oxidation of VOC.
Student: Liliana Patricia Castro Rodriguez
Adviser: Adriana Echavarría Isaza
.
Doctoral Seminar II.
The design of catalytic systems for controlling of volatile organic compounds (VOC)
emissions is regarded as one of the most significant instruments for environmental
protection. It is known that thermic combustion and catalytic oxidation methods are
the most widely used for the elimination of VOCs. Thermal oxidation is suitable for
removing VOCs from flue gas streams with a high flow rate and a high concentration
of its. More than 99% of the VOCs can be burned by thermal combustion, typically
at high temperatures (>1000 ºC), obviously that process requires large amounts of
energy and the use of ceramic materials. On the other hand, in the catalytic oxidation
is required a catalyst in order to decrease the activation energy and subsequent
reduction of reaction temperature. The main differences between thermal
combustion and catalytic oxidation process are lower operation temperature,
typically between 180ºC - 400ºC, and the need of a catalyst.
This temperature
reduction may result in lower operation cost (1,2,3).
Catalysts for VOCs are based on noble metal oxides and transition metal oxides
and/or mix of them. The active metal oxides are deposited on an appropriated
support, finally the catalyst activity could be affected by the surface reactivity and the
microstructure of the support.
It has been pointed out that the catalytic oxidation of VOCs has been achieved at
lower temperatures using hydrophobic supports (activated carbon, CNT, CNF). The
water vapor produced during the oxidation reaction damages the active sites of
inorganic catalyst. For this reason, some authors have compared the catalytic
behavior for oxidation of toluene with tungsten oxide deposited on different supports
as activated carbon, aluminum, silicon and titanium oxides and USHY zeolite (4),
(5). Likewise, Morales-Torres and co-workers have compared the performance of
the catalysts Pd and Pt supported on carbon nanofibers (CNF) - coated monoliths
and on γ-Al2O3 coated monoliths in the catalytic oxidation of benzene, toluene and
m-xylene. In both researches, they found that carbon materials were better supports
than inorganic support for this reaction (6). Besides, Shujuan Zhang and co-workers
studied the catalytic performance of cobalt oxide supported on carbon nanotubes
(CNTs) (7). They observed that structural defects on surface of CNTs could improve
the catalytic activity of Co3O4/CNTs to achieve complete oxidation of toluene at low
temperature.
Finally, carbon materials are a good alternative as support of efficient catalysts for
catalytic combustion of VOCs and the support can be improve by tuning the surface
structures of CNTs.
References.
1) W.B. Li , J.X. Wang a, H. Gong a . Catalytic combustion of VOCs on non-noble metal
catalysts, Catalysis Today 148 (2009) 81–87 .
2) Marco Tomatis, Hong-Hui Xu, Jun He, and Xiao-Dong Zhang. Recent Development of
Catalysts for Removal of Volatile Organic Compounds in Flue Gas by Combustion: A Review
.Journal of Chemistry. 2016, 1-15.
3) Wenxiang Tang, Gang Liu, Dongyan Li, Haidi Liu, Xiaofeng Wu, Ning Han & Yunfa Chen
Design and synthesis of porous non-noble metal oxides for catalytic removal of VOCs.
Science China Chemistry, September 2015, Vol.58, No.9. 1359-1366.
4)
W.B. Li, J.X. Wang a, H. Gong a . Catalytic combustion of VOCs on non-noble metal
catalysts, Catalysis Today 148 (2009) 81–87 .
5) M.A. Alvarez-Merino, M.F.Ribeiro, J.M.Silva, F.Carrasco-Marín and F.J. Maldonado-Hodar.
Activate Carbon and Tungsten Oxide Supported on Activated Carbon Catalysts for Toluene
catalytic Combustion. Environ. SCi.Technol. 2004,38,4664-4670.
6) S. Morales-Torres , A.F. Perez-Cadenas , F. Kapteijn F. Carrasco-Marín F.J. MaldonadoHo ́ dar , J.A. Moulijn. Palladium and platinum catalysts supported on carbon nanofiber
coated monoliths for low-temperature combustion of BTX . Applied Catalysis B:
Environmental 89 (2009) 411–419
7) Shujuan Jiang, Shaoqing Song. Enhancing the performance of Co3O4/CNTs for the catalytic
combustion of toluene by tuning the surface structures of CNTs. Applied Catalysis B:
Environmental 140-142 (2013) 1-8.