Chemical composition of the Earth's mantle phases have a major effect on their stabilities and consequently on their reactions. Especially concerning light elements and trace elements, compositions of phases in the lower mantle remain basically unknown because the phases are not accessible and cannot be studied directly. In order to betterlearn about reactions of mantle phases, related redistribution processes of elements and the resulting properties of the mantle, mantle phases have been studied by in-situ methods.Within the past years, laser-heated diamond anvil cells have been combined with synchrotron radiation induced methods to study chemical reactions by in-situ x-ray fluorescence analysis and combined x-ray diffraction (XRD) (Petitgirard et al., 2012). Synchrotron radiation provides sufficiently small spot sizes, hard x-rays and a high sensitivity.Chemical and structural information were obtained at temperatures of up to 4200 K and pressures up to 130 GPa. First time-resolved measurements have been made with the objective to follow reaction mechanisms. For XRD, a time-resolution of msec could be achieved by single shot pulsed laser heating (Goncharov et al., 2011), while for insituXRF studies, the time-resolution is currently limited to the sec regime. It is either limited by detector speed or sensitivity or both.An alternative method to study reactions of lower mantle phases are laser-driven shock and ramp compression experiments. The samples are generally pumped with an long-pulse optical laser and then probed with an x-ray source at a delayed period. Combined with x-ray free electron lasers as a probe beam, these experiments offer the uniquepossibility to study reactions at a rate of up to MHz due to the x-ray timing structure and the increased number of photons. The High Energy Density science instrument at the European XFEL (HED) will provide unique possibilities for research at extreme states of matter. The instrument is one of the six baseline instruments at the European XFEL andwill start user operation in the second half 2017.In this presentation, we will show results from in-situ experiments at conditions in the lower mantle at currently available sources and discuss the persectives to study reaction mechanisms at such conditions at the upcoming HED instrument.