Quantitative 31 P solid-state nuclear magnetic resonance spectroscopy ( 31 P-MAS-NMR) of X-HCP-Ru (Fig ) reveals the presence of oxidized phosphorus atoms (δ = 22.4 ppm) with a proportion of 39 % of all phosphines. The majority of the phosphines (δ = -17.3 ppm) remains non-oxidized (61 %), whereby the peak consists of a sharp one from the ordered domains and a broader part, resulting from less ordered domains. X-ray photoelectron spectroscopy (XPS) emphasizes the partial oxidation of the phosphines and suggests that 29 % of the phosphines are oxidized. This quantification roughly matches to the NMR results, considering that XPS measurements overrepresents near-surface areas and not the overall bulk phase (Fig. and Fig. ). Due to the low metal loading and the overlapping with the dominant C1s peak, XPS does not enable an unambiguous electronic specification of the ruthenium species (Fig. ). The X-HCP-Ru catalyst was applied in the base-mediated CO2 hydrogenation reaction to formic acid, where a TOF of 1249 molFA molRu h -1 was obtained. In order to put the catalytic performance in context, reference experiments were carried out (Fig. ). The (Ru)-metal-free X-HCP was inactive. Additionally, a comparable HCP network without phosphine units, which contains solely crosslinked BCMBP units, was synthesized and afterwards impregnated with ruthenium by ligand exchange (BCMBP-HCP-Ru). BCMBP-HCP-Ru showed a negligible activity, which reveals the involvement of both species, the phosphine microenvironment and the metal center, in the catalytically active species of X-HCP-Ru. A low activity was observed for the commercial Ru@C as example for a heterogenous catalyst and the homogenous Ru(NO)(NO3)3 complex. Since the Xantphos ligand is barely soluble in the aqueous phase, the reference reaction of the Xantphos ruthenium complex was carried out in DMSO with NEt3 as a base. The resulting TOF of 577 molFA molRu h -1 lies in a comparable range as other reported homogeneous biphosphine ruthenium complexes. These reference experiments emphasize the remarkable performance of X-HCP-Ru. The catalytic stability of X-HCP-Ru was investigated by recycling experiments (Fig. ), where the solvent was exchanged after each recycling step. Over the first and second run, a continuous deactivation of the X-HCP-Ru is observed, resulting in a significant drop of the catalytic productivity after 5.5 hours. Since the hydrogenation reaction is far away from thermodynamic limitations, it can be associated to a gradual degradation of the catalytic species. Starting from the third run, a nearly linear slope with a minor decay of the productivity occurs. Thus, the X-HCP-Ru forms a stable catalyst after a certain induction period, which coincides with findings about comparable catalytic systems for the CO2 hydrogenation reaction to formic acid. In order to investigate the initial degradation, the retained X-HCP-Ru after four catalytic runs was further analyzed and compared to the pristine X-HCP-Ru. P-MAS-NMR (Fig. ) shows no significant increase in the proportion of oxidized phosphines (from 39 to 43 %). ATR-IR does not indicate any structural changes of the network (Fig. ). In TEM images (Fig. ) no agglomeration of the dispersed metal species was noticed. In contrast to previous works, leaching of active species could be excluded as origin of the catalyst degradation. While the filtrate contains negligible amounts of ruthenium (0.2 wt-ppm) and phosphorus (0.5 wt-ppm) (Table ), the hot leaching experiment clearly indicates no catalytic conversion after the removal of X-HCP-Ru, proving its heterogeneous nature (Fig. ). Kann et al. proposed the formation of ligating carbon monoxide as reason for the catalytic degradation, whose retarding influence was mentioned by Jessop et al.