Try to crush your catalyst to make the homogenization easier. Then mix it well and grind it. Use the appropriate solvent to for the extraction. 

If you provide more information about the catalyst and what exactly you want to study perhaps I or other persons can give you more specific answer.

Thank you Dr. Rafał Gałązka for your answer

my catalyst is carbon and CNT doped nickel oxide

Dear G. Abdulkreem Ghassan ALSULTAN

First of all, I am not a doctor. I am just a technician working as chemical analyst ;-)

Secondly, I presume that you would like to measure the amount of certain elements that are washed out from your catalyst during some process you are performing. Am I right?

If yes, then as an extractor, I would use substance that is going though this catalyst during this process to check what is leached from the catalyst. Just make sure that this substance is of high purity to measure what is leached not is in the substance prior to leaching. In this case, I think, crushing and grinding is not necessary as you will simulate the process.

If you want to measure the content of elements in the catalyst. Then you will have to dissolve the catalyst in strong acid(s) (preferably HNO3, HCl or Aqua Regia. In this case you will probably get much higher contents of elements than in previous case.

The method of extraction of elements from catalyst depends on what exactly you want to measure. For example, if you want to measure the most mobile elements, try to run distilled water through the catalyst and see if this has increased the content in water. If you want to check the elemental composition, try digestion with strong acids.

I do not know the details of the process so the above are just my guessing. Hope this help a little.

PFA the general protocol