Hi all,
CO is one of the major air pollutants which toxic. Most of the literature says catalytic oxidation as a removal remedy for CO, by using catalysts especially Pd in nano size. Can anybody tell why the nano dimension is required for CO oxidation? What will happen if the catalyst size is micro in size and why?
Also, is there any other way of removing CO than catalytic oxidation? If yes, then what is the advantages of catalytic oxidation of CO over the other methods?
Thanks in advance,
ANSARI P
Dear Ansari Palliyarayil,
your question is so simple that you yourself could easily answer it if you thought a little.
The catalyst allows the oxidation of carbon monoxide at low temperatures, since it reduces the activation energy of the reaction 2CO + O2 = 2CO2
Of course, carbon monoxide can be oxidized without a catalyst, but this will require higher temperatures than, for example, in the exhaust system of a car. The efficiency of the catalyst is the higher, the larger its specific surface area (the ratio of surface area to mass). For this reason, the use of nanosized catalyst powders allows one to save its amount (coarser-grained catalyst powders are also quite workable, just the larger the particle size the more mass of precious metal is required to oxidize the same amount of carbon monoxide).
Dear Ansari Palliyarayil ,
Reactions take place at the surface of materials. Therefore, the higher the surface/volume ratio, the more efficient your catalytic process is. So, Pd nanopowder is better than micropowder.
Ansari Palliyarayil
I will add some details to the good answer Vadim Verlotski . Stages of heterogeneous catalysis:
1) diffusion of the reaction participants to the catalyst surface;
2) adsorption of the reaction participants on the surface;
3) chemical reactions between adsorbed substances;
4) desorption of reaction products.
Activation energy is a certain excess amount of energy (compared to the average) required for a molecule to react.
The theory of active collisions is a theory according to which only molecules with an energy greater than the activation energy react in an elastic collision of molecules.
Thus, the larger the specific surface area, the more CO and O2 molecules are adsorbed on the catalyst, the catalyst decreases the activation energy, the proportion of active molecules becomes larger, and the reaction rate increases.
I am attaching an article on this topic.
Article Preparation of Nanomaterials from Aqueous Solutions Imitatin...
Dear Ansari Palliyarayil ,
CO is found in a gaseous state and highly soluble in an aqueous medium. Oxidation is the best possible way for its removal. Nano Pd is good for its oxidation because of its high catalytic property and high S/V ratio. Apart from Pd, various other metals or mixtures (Au|TiO2, Au|Al2O3) could be used for its oxidation.
Attaching the article for reference:
Article CO Oxidation Kinetics over Au/TiO2 and Au/Al2O3 Catalysts: E...
Thank you Vadim Verlotski, Jose Miguel, Yuri Mirgorod, and Sai Prasad for your kind response.
Other than oxidation, is there any other way for removing CO?
Vadim S. Gorshkov
Thank you for your response. Is there any other possible mode of CO removal, other than by using catalysts? I mean methods like adsorption?
Mao, Xinyu, Alexandre Foucher, Eric A. Stach, and Raymond J. Gorte. "A study of support effects for CH 4 and CO oxidation over Pd catalysts on ALD-modified Al 2 O 3." Catalysis Letters 149, no. 4 (2019): 905-915.
Since Pd is considered as a noble metal, hence nano structuring will reduces the metal consumption, and costs, making the procedure economic, while improving the performance.
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