In the industrial practice of volatile organic compounds (VOCs) purification, it is generally accepted that the performance of precious metal catalysts is highly related to precious metal’s concentration. For this reason, many catalyst users only care about precious metal’s concentration and neglect the performance of catalysts. Maybe they even don’t know what they are purchasing, precious metal or catalyst.
As is well known, catalysts are high technical products. Developing a high-performance catalyst often takes 3-5 years or more due to complexity of affecting factors，such as the ratio of metallic state to oxidized state of precious metals, the exposed crystal surfaces of active components and the interaction between active components and supports,etc.How do these key factors affect catalyst’s performance? In the past ten years, the research team led by Professor LuoMengFei, the founder of Progre Catalysis(PC), had a deep research on this issue and found that catalysts with the same precious metal’s concentration may exhibit vastly different performance due to differences in formulations and preparation techniques.
Prsence form of precious metal
The active site for CO oxidation is PdO. The activity of PdO decreases when it enters into CeO2 lattices and forms solid solution. However, its activity of CH4 oxidation is just the opposite. PdO entering into CeO2 lattices to form solid solutions has high activity. It can be seen that the presence form of Pd has a significant impact on the catalytic oxidation activity.
Figure 1
Support and promoter
The catalytic performance for propane(C3H3) and carbon monoxide (CO) was tested by loading the same amount of Pt (1wt%) on two different supports,CeO2 and Nd2O5, respectively. From the Figure 2 (Journal of Physical Chemistry C, 2021, 125: 19301-19310), we can find that the activity of Pt/Nd2O5 catalyst is better than that of Pt/CeO2 catalyst for C3H3 oxidation, and the activity of Pt/CeO2 catalyst is better than that of Pt/Nd2O5 catalyst for CO oxidation.
Figure 2
Next, let's take a look at the effects of promoters. Figure 3 summarizes that the concentration of precious metal and promoter affects propane oxidation performance of Pt/ZSM-5 catalyst. From Figure 3(a), it can be seen that the concentration of precious metals is helpful in improving the performance of catalysts, but there is no effect when it exceeds 1wt%. which means that there is a threshold for the effect of precious metal’s concentration on catalyst’s performance. From Figure 3(b), we can easily observe that different components have different impact on the activity of the catalyst. W has a very significant promoting effect on the activity of Pt/ZSM-5 catalyst, while other components(Nb, Ce, Mo) have an inhibitory effect.Moreover,when the addition amount of W is 3W, the catalyst has the highest activity (Figure 3(c)).
Figure 3
Particle size
It can be clearly seen from Figure 4 that the activity of the catalyst is closely related to the particle size of Au (Journal of Catalysis, 2016, 37:1580). With the same concentration of precious metal, the activity of the catalyst can vary by dozens times due to difference in particle sizes.
Figure 4
