There is a simple process to export your current product catalog from nopCommerce into ShopTab to create a Facebook storefront in your Facebook Fan Page to sell your products.
In nopCommerce go to Administration Panel > Catalog > Products > Manage Products
Select the option " Export to Excel (all)" - This will export all the products in your store database in an excel CSV file. Save the file. Make sure you have the following fields - title, description, price, category, URL to product page, URL to image(s).
Reference link in nopCommerce forum.
Once the file is created, you can upload the CSV file in ShopTab.