Nanoparticle exsolution is regarded as a promising alternative to classical catalyst synthesis routes. In this work, we compare the catalytic performance of nanoparticles formed by in-situ exsolution during dry reforming of methane with particles pre-formed by reductive pre-treatment. The experiments were conducted on three perovskite-type oxides. Using a combination of in-situ and operando spectroscopic investigations (x-ray diffraction, near ambient pressure x-ray photoelectron spectroscopy) and the correlation to the obtained catalytic results, we could highlight that pre-formed nanoparticles strongly enhance the activity compared to in-situ exsolution. Scanning electron microscope images recorded after catalytic tests revealed that nanoparticles formed during reductive pre-treatment are bigger on average than particles formed in-situ. Furthermore, B-site doping with Co or Ni significantly enhanced the catalytic activity. Importantly, the perovskite host lattice was stable in all experiments, thus providing the necessary enhanced oxygen surface chemistry which is the key to the coking resistance of the investigated materials. Additionally, we observe a temperature dependent change of mechanism leading to different product ratios.