Nanostructured nickel-based catalysts have been produced by solution combustion synthesis (SCS) and it has been found that their physical properties and atomic structure depend in a complex way on the parameters of SCS processing, especially the amount of water used in the initial solution. The catalysts were characterized by XRD, BET, and GC-IRF and their catalytic activity for hydrogenation of maleic acid was determined. Various mechanisms (especially at the atomic level) are active during these materials syntheses that critically influence their catalytic properties, often in opposing ways. Hydrogen adsorption studies have helped to clarify the main mechanisms involved. Specifically, it was determined that nickel oxide acts as a carrier for nanostructured metallic nickel, in the absence of which the catalyst almost deactivates. Understanding the interrelationships between the processing parameters and the ensuing atomic structure has allowed a degree of optimization of the catalytic properties of the new catalysts. (C) 2016 Elsevier Inc. All rights reserved.