This short article provides reflections on a most productive collaboration between the authors and Dr. J.C. Volta as an appreciation to mark Jean Claude's retirement in 2006. The sole topic that we focused on during 15 years of intensive effort was a study of vanadium phosphate catalysts, a topic that all of us have found fascinating and challenging, as have many other scientists in the last 50 years. Aspects of the key research themes, in particular the role of amorphous VPO phases, are revisited. (c) 2007 Elsevier B.V. All rights reserved.