Source: Guardian UK
My Spanish is a bit rusty, but the Excelsior (Mexico) and 20Minutos (Spain) label him a 'chemical technician' and 'chemical engineer' respectively. Lisa Balbes helpfully points out that, according to ABC News, one of his first assignments in the church was teaching high school chemistry.
I tried to look up the Pope's peer-reviewed chemistry publications through SciFinder, Reaxys, and Google Scholar, but, alas, I'm unable to find any. Perhaps a more enterprising reader can clue me in if they're more successful...
*Though I'm not Catholic, I appreciate the influence and direction the Pope offers the faithful. I also find it exciting when chemists enter very public walks of life. See, for example, Jack Welch, Angela Merkel, or John Kuhn.