There are many books about preservation of framed art, documents, photos and objects. This is in no way a comprehensive treatment.
In general, the contents of the framing package (backer board, mounting board, mats, etc.) should be acid free. Even if the art or item being framed is acidic this is generally the rule to prevent the package contents from degrading over time. If the art, document or photo is on an acid free substrate (paper) this is especially true as the acid from non-acid-free items will migrate to the acid free item and cause deterioration.
There are products that are acid free and that also contain zeolytes. Zeolytes provide additional protection in that this chemical actually traps acids and many other pollutants within the cell structure, preventing the acid or pollutant from migrating further.
-- Always do the Right Thing the Right Way the First Time - if you can figure out what that is! Ken, Spring Branch, TX