WASHINGTON, Dec 23 (Reuters) - The U.S. Department of Energy said on Thursday it has offered Monolith Nebraska LLC an up to $1.04 billion conditional loan guarantee for a project to make clean hydrogen, which can be used to make fertilizer.

The loan guarantee will help Monolith expand its Olive Creek plant to convert natural gas into hydrogen for making products like fertilizer.

It will also make carbon black, a product used in making tires and other rubber products. The project aims to reduce carbon emissions by cutting the use of fuel oil to make those products, the department said. (Reporting by Timothy Gardner Editing by Chris Reese)