Can someone patent something that has already been released in a sell catalog by a company within the past 6 months

The below does not constitute legal advice, does not form an attorney-client relationship, and should not be relied upon to take or refrain from taking any action.

In the United States, a patent may still be able to be applied for under these facts. An inventor has up to 1 year after the first public disclosure, sale, or offer for sale of the invention to file a patent application (assuming the inventor(s) can show they conceived of the invention before that first disclosure). If an application is not on file after a year, the inventors are barred from obtaining a patent in the United States. Most other countries require absolute novelty, meaning a patent application must be on file before the first public disclosure of the invention, so assuming no application was on file when the advertisement was made, foreign patents are almost certainly not possible.

Implicit in the question is whether someone can "take" the idea and patent it. In the United States, only the inventors of a patentable idea may apply for a patent on the idea. So, if someone were to have just happened upon the trade show and saw the product, that person would not be able to patent it themselves, as they did not actually make the invention. As a practical matter, however, it is difficult for the USPTO to discover that kind of behavior. Even assuming a patent issued under those circumstances, it would be invalid based on the earlier disclosure and naming incorrect inventors.

If the first publication occurred six month ago, then the inventor has up to one year to present a Patent application in the USA. All other countries are barred.
If besides this catalog, there was disclosure that add up to more than one year, then the inventor is barred from obtaining a patent

Let me expand of the fact pattern. How about a product that is manufactered in a way under a trade secret process. If an independant inventor creates that process and has not tried to sell it themself, creates the exact same process, and submits it for a patent. S/he will be granted a patent, and the original company will be precluded from obtaining a patent.
Companies use trade secrets when they believe others will not figure it out, and good examples are brand name sode products, etc.
To answer your question yes it is possible. But in this case, infringement is a completely different issue.