As far as Google is concerned, product rich snippets aren't supported in product listings:
Use markup for a specific product, not a category or list of products.
See Google Rich snippets - Products
Search Engine Journal offers some good advice that more specifically answers your question though:
Depending on how the website is set up, you may choose to mark up
category pages. If you list product information on the category pages,
you will want to omit any microdata markup as it may cause a
confliction with the product pages. After all, the goal for
conversions usually starts with the product pages, so you will want
the product page to be the landing page rather than a category page.
For a simple category page that lists category names, place each
category name in an h1 tag and add the following microdata markup.
See E-Commerce Microdata Best Practices under the Category Page Markup heading.
Their reccomendation, and it seems a good one, is to add markup to your product list template somewhat like this:
<ul id="category_list">
<li itemscope itemtype="http://schema.org/Enumeration">
<img src="http://url.to.image" itemprop="image" />
<h1 itemprop="name">Category Name</h1>
</li>
</ul>