Hi everyone,
I am applying a heterogeneous catalyst system, I mean solid catalyst. When I use a huge amount of this catalyst, the catalytic activity decreases sharply. I'm thinking about the compete interaction phenomenon between these catalyst particles to each other, because I think the catalysis must always be preceded by the adsorption (the reagent moleculars interact to the catalyst surface). Actually, I try to find a suitable way to explain and feel so confused. So can you help me to resolve this issue?Thank you.
Yea, The amount of heterogeneous catalyst can affect on the catalytic activity. Optimized concd. is essential for activity in mole%.
I think you're on the right track in explaining the integrated and competing effects of mixing different types of solid-state catalysts.
I'd also add that one catalyst could poison the active sites of another catalysts and could plug the pores of each other. The intent of adding a catalyst is to lower the reaction activation energy (E*) to enhance the kinetics of the reaction of interest. When you mix different catalyst together, the integrated effect on the reaction's activation energy may be less effective compared to a single catalyst.
Hope this helps answer your question.
Professor Yehia Khalil, Yale University, USA
Fellow of the University of Oxford, UK
Thank you very much.
Dear Prof.Yehia Khalil, your answer hepls me understand clearly about the basic chemical knowledge, integrated and competing effects, specially. Thank you.
Activity depends on the method used to measure it and of the geometry of the reactor. The conversion does not increase proportionally to the contact time with the catalyst because the concentrations (or the partial pressures) of the reactants decreases and the concentrations of the products, which can slow down the reaction, increases. The geometry of the reactor has an effect because it modifies the mass transfers. As noted by Eslam Gomaa Al-Sakkari, the reaction can become mass transfer controlled when the amount of catalyst increases.
Dear Xuemin Li,
Actually I just only use 1 catalyst in my catalytic system
We are using heterogeneous catalyst in our plant. The use of excess catalyst can increase the reaction rate and cause byprouct formation or decomposition of main products. The byproducts or decomposed products some times may be tarry substances. They will deposit on catalyst and may be causing decrease in catalyst activity or they may be acting as poisons and decreasing catalyst activity.
Dear Govardhana Rao Muthineni, thank you, I also think about that phenomenon, so I think I can try to caculate the Selectivity. Because maybe, the use of excess catalyst can cause byproduct formation or decomposition of main product. Thank you for your opinion.
Dear Huyen Tran Dang do not confuse between activity and selectivity. They have different meanings. A catalyst can have higher activity and lower selectivity. Please try to maintain proper reactants and catalyst ratio otherwise sometimes runaway reactions took place and reactor will blast
Dear Huyen Tran Dong, you may try to optimize the catalyst loading with respect to the reactants first, and then try to also optimize reactor parameters. What Govardhana said is very helpful or even the solution to your problem
You can find the optimum condition for the amount of catalyst and selectivity. You should try to many experiments to do so. best wishes
Dear Ali Al-Rubaie, actually I've already found out the optimum condition for the amount of the catalyst, then I try to change the amount of the catalyst, and then try to find an explaination for that phenomenon. But anyway I think all of your opinions are really treasure and they can help me find solutions.
Dear Huyen, in fact this phenomenon happened to me in my recent search. When I increase the dose of catalyst, degradation incresed sharply until it reaches 2 g / l. But when i used a high dose (4 g / l) , the degradation decresed suddenly. when the catalyst loading exceeded the limiting value (2 g/l ), the degradation rate would decrease due to two reasons. The first reason is the increase in turbidity and
light scattering at high photocatalyst concentrations which lead to a decrease in the light path inside the solution. The second one is the aggregation of the catalyst itself which causing a decrease in the number of photocatalytic active sites on its surface. you can see this in details in our search
http://pubs.rsc.org/en/content/articlehtml/2017/ra/c6ra27957k
good luck
This is mainly due to the agglomeration (particle-particle interactions) which tend to decrease the exposed surface area of the catalyst active sites
- Badges
- Science topic
- Similar topics
- Engineering
- Chemical Engineering