Hi Welcome to the forum, the 2.8iTD has a timing belt like most of the engines (1.9,2.0 2.5 & 2.8JTD) fitted to Ducatos over the years. I am sure someone will correct me if not the case but the only engines with a chain are the 2.2ltr & 3.0ltr multijet. The current 2.3ltr has a belt which drives the inlet camshaft & drive is transmitted to the exhaust camshaft via a chain at the rear of the cylinder head.
Cheers