Tuning the Cerium-Based Metal–Organic Framework Formation by Template Effect and Precursor Selection
Dimitry Grebenyuk, Maria D. Shaulskaya, Artem Shevchenko, Mirijam Zobel, М. А. Тедеева, Alexander L. Kustov, Ilia I. Sadykov, Dmitry Tsymbarenko
Abstract
High Resolution Image Download MS PowerPoint Slide The novel metal–organic framework [(CH 3 ) 2 NH 2 ] 2 [Ce 2 (bdc) 4 (DMF) 2 ]·2H 2 O ( Ce-MOF, H 2 bdc─terephthalic acid, DMF─ N, N -dimethylformamide) was synthesized by a simple solvothermal method. Ce-MOF has 3D connectivity of bcu type with a dinuclear fragment connected with eight neighbors, while three types of guest species are residing in its pores: water, DMF, and dimethylammonium cations. Dimethylamine was demonstrated to have a decisive templating effect on the formation of Ce-MOF, as its deliberate addition to the solvothermal reaction allows the reproducible synthesis of the new framework. Otherwise, the previously reported MOF Ce 5 (bdc) 7.5 (DMF) 4 ( Ce5 ) or its composite with nano-CeO 2 (CeO 2 @ Ce5 ) was obtained. Various Ce carboxylate precursors and synthetic conditions were explored to evidence the major stability of Ce-MOF and Ce5 within the Ce carboxylate-H 2 bdc-DMF system. The choice of precursor impacts the surface area of Ce-MOF and thus its reactivity in an oxidative atmosphere. The in situ PXRD and TG-DTA-MS study of Ce-MOF in a nonoxidative atmosphere demonstrates that it eliminates H 2 O and DMF along with (CH 3 ) 2 NH guest species in two distinct stages at 70 and 250 °C, respectively, yielding [Ce 2 (bdc) 3 (H 2 bdc)]. The H 2 bdc molecule is removed at 350 °C with the formation of novel modification of Ce 2 (bdc) 3, which is stable at least up to 450 °C. According to the total X-ray scattering study with pair distribution function analysis, the most pronounced local structure transformation occurs upon departure of DMF and (CH 3 ) 2 NH guest species, which is in line with the in situ PXRD experiment. In an oxidative atmosphere, Ce-MOF undergoes combustion to CeO 2 at a temperature as low as 390 °C. MOF-derived CeO 2 from Ce-MOF, Ce5, and CeO 2 @ Ce5 exhibits catalytic activity in the CO oxidation reaction.