We chose this MOF due to its high predicted ideal ethane/ethylene selectivity. Additionally, La-BTC has a simple, one-step synthesis from commercially available reagents. We confirmed synthesis of the intended structure by powder X-ray diffraction (PXRD) and compared the measured diffraction pattern to a pattern predicted by Mercury (see Sec. 2 and Supporting Information Figure ). We observe fairly good alignment between the predicted and experimental diffraction patterns, although with a few additional peaks. From X-ray photoelectron spectroscopy (XPS), MOF elemental composition was found to be 4.9:61.0:34.1 La:C:O, compared with a theoretical ratio of 6.2:56.3:38.5 (Supporting Information Figure ). The carbon region of the XPS spectrum appears to predominantly contain C-C and O-C=O bonds, to be expected from the BTC linker. Similarly, we observe primarily C=O and C-O bonds in the oxygen region of the spectrum, again from the BTC linker. In the La region of the spectrum, we observe 3/2 and 5/2 multiplet splitting but no obvious peaks to indicate the formation of compounds such as La2O3 or La2(CO3)3. If such species are present, they are only very minor products. We believe these findings indicate the majority of the sample is likely the intended structure. However, there may also be some free benzene tricarboxylate linker that became trapped in the pores during synthesis and could not be removed during the subsequent washing steps. The trapped linkers may lower the available surface area for adsorption compared to a pristine crystal.