This perspective summarizes results of in situ adsorption and reaction experiments on graphene-supported nanoparticles: the particular aim is to point out similarities and differences between studies on "traditional" single crystal studies and the more complex, more realistic nanoparticles. It is shown that the use of quantitative X-ray photoelectron spectroscopy allows for gaining a detailed insight even into these complex systems, thereby facilitating a further step into bridging the materials gap from fundamental science to applied sciences. The use of graphene as a substrate gives intriguing new possibilities, as the template effect of graphene can lead to a very narrow size distribution of the clusters, while graphene itself is chemically innocent, thereby making side processes such as spill over and reverse spill over less likely. The systems discussed range from extremely well studied systems such as the adsorption and reaction of CO on a Pt(111) surface, to stepped surfaces and finally to nanocluster arrays supported on a graphene support. Also, the important chemistry of sulfur, being a strong catalyst poison, on such systems will be discussed. While the adsorption behavior on nanoclusters is strongly reminiscent of the adsorption on stepped surfaces, a strong increase in the reactivity of nanoparticles systems is found. [GRAPHICS]