How can I download images from my WhatsApp Business catalog link using Dropbox?

I was looking for the same information and found your question. When I couldn't find an answer online what I did (and it worked) was to go to the picture in the whatsapp catalogue that i want (all online not through the app), I right click on it , choose copy image, I had a blank word document open, pasted it in the word document, then right click the pasted picture in word , choose save picture as, and the save as box will appear, choose a file to save and there you go! you have it in your file. 

Hope this helps :-)