UPDATE: Extension updated of Opencart 4.0
Mintegra Bulk Sitemap XML builder build the sitemap for your opencart website.
Sitemap builder can be configured to build following
1) Products - sitemap xml for products
2) categories - sitemap xml for categories
3) Category Products - Sitemap xml for category products
4) Manufacturers - Sitemap XML for manufacturers
5) Information - Sitemap XML for information pages
Uses gz to compress the xml files and maps all the Sitemap child xml files to a parent Sitemap.XML to be submitted to google.
We have submitted successfully 100k plus links to google using this sitemap generator.