In Situ Neutron Diffraction of Zn-MOF-74 Reveals Nanoconfinement-Induced Effects on Adsorbed Propene

Even though confinement was identified as a common element of selective catalysis and simulations predicted enhanced properties of adsorbates within microporous materials, experimental results on the characterization of the adsorbed phase are still rare. In this study, we provide experimental evidence of the increase of propene density in the channels of Zn-MOF-74 by 16(2)% compared to the liquid phase. The ordered propene molecules adsorbed within the pores of the MOF have been localized by in situ neutron powder diffraction, and the results are supported by adsorption studies. The formation of a second adsorbate layer, paired with nanoconfinement-induced short intermolecular distances, causes the efficient packing of the propene molecules and results in an increase of olefin density.


S1
Table S1: Crystallographic data of activated Zn-MOF-74-0, space group R-3, a = 25.9754(14), c = 6.8408(6),V = 3997.2(6)                From this set of experiments, the activation energy of desorption (E A_des ) from the OMS was determined.However, this method is not suitable for the determination of E A_des of the additional two adsorption sites.It can be shown that the temperature of a peak maximum T p of a first-order desorption process follows: Where A is the preexponential factor and R is the universal gas constant.Therefore, plotting ln(β/T p 2 ) versus 1/T p yields a linear function where the slope corresponds to E A_des . 3To obtain reasonable results, β must be varied over at least one order of magnitude. 3It is important to note that (1) is only valid if the site coverage is identical for all experiments and the peak maximum coverage is independent of β.These assumptions are reasonable for most desorption processes performed on saturated materials.

Figure S1 :
Figure S1: PXRD pattern (a) and nitrogen physisorption isotherm (b) of Zn-MOF-74.In the right graph, squares and diamonds correspond to data points of the adsorption and desorption branch, respectively.

Figure S13 :
Figure S13: Measured loadings as refined against the approximated loadings dosed.The error bars reflect three standard uncertainties of the measured loading as refined from the NPD data.Data collected at 226 K.

Figure S14 : 3 )Figure S15 :
Figure S14: Cell parameters as a function of the approximated loadings.The error bars reflect three standard uncertainties of the refined cell parameters.Data collected at 226 K.

Figure S16 :
Figure S16: Local structure in a fraction of the pore of Zn-MOF-74-8_1K.Propene molecules of the first adsorption layer (P1, P2, P3) are drawn with yellow bonds, while second-layer propene molecules (P4) feature dark blue ones.The adsorption of propene molecules to Zn(II) sites (cyan spheres) is depicted by purple lines, while the distances Zn-C 1 and Zn-C 2 are represented in a darker shade of purple.The C 2 -C 2 distance between a molecule of the first and one of the second layer is displayed in cyan, whereas the shortest distance is shown in dark blue.Color code: grey, C; white, H; green, D; red, O; cyan, Zn.

Figure S18 :
Figure S18: TPD experiments of propene-charged Zn-MOF-74.The TCD signal was recorded as a function of time, requiring the normalization by 10/β.1,2The colors correspond to different heating rates: light blue (1 K/min), dark blue (2 K/min), green (5 K/ min), and red (10 K/ min).In the inset, ln(β /T p 2 ) versus 1/T p is plotted, such that the activation energy of desorption can be deduced from the slope as 42(5) kJ/mol.

1 S21Figure S19 :
Figure S19: Physisorption of propene at 215 K with squares and triangles corresponding to the adsorption and desorption branch, respectively.

Table S2 :
Crystallographic data of Zn-MOF-74-1, space group R-3, a = 25.9747(13),c=6.8420(6),V = 3997.7(5),goodness of fit parameters, Rwp = 2.63770527, Rexp = 1.13349137,GoF = 2.3270625.Values in parentheses display the standard uncertainty of the refined value.Data collected at 226 K. Atoms with containing "f" and "p" in the label correspond to framework and propene, respectively.In the case of the propene atoms, numbers that are not bracketed depict the corresponding propene molecule, while bracketed numbers indicate the position within the molecule.E.g.Cp1(2) is carbon atom 2 in propene molecule 1.

Table S3 :
Crystallographic data of Zn-MOF-74-2, space group R-3, a = 25.973(2),c=6.8440(9),V=3998.3(8),goodness of fit parameters, Rwp = 3.41087084, Rexp = 1.10388183,GoF = 3.08988766.Values in parentheses display the standard uncertainty of the refined value.Data collected at 226 K. Atoms with containing "f" and "p" in the label correspond to framework and propene, respectively.In the case of the propene atoms, numbers that are not bracketed depict the corresponding propene molecule, while bracketed numbers indicate the position within the molecule.E.g.Cp1(2) is carbon atom 2 in propene molecule 1.

Table S5 :
Crystallographic data of Zn-MOF-74-6, space group R-3, a = 25.9279(15),c=6.9093(7),V = 4022.5(6),goodness of fit parameters, Rwp = 2.73434503, Rexp = 1.42730079,GoF = 1.91574548.Values in parentheses display the standard uncertainty of the refined value.Data collected at 226 K. Atoms with containing "f" and "p" in the label correspond to framework and propene, respectively.In the case of the propene atoms, numbers that are not bracketed depict the corresponding propene molecule, while bracketed numbers indicate the position within the molecule.E.g.Cp1(2) is carbon atom 2 in propene molecule 1.

Table S7 :
Crystallographic data of Zn-MOF-74-8_1K, space group R-3, a = 25.8956(15),c=6.9200(6),V = 4018.7(6),goodness of fit parameters, Rwp = 2.8709897, Rexp = 0.834896507, GoF = 3.43873723.Values in parentheses display the standard uncertainty of the refined value.Data collected at 1 K. Atoms with containing "f" and "p" in the label correspond to framework and propene, respectively.In the case of the propene atoms, numbers that are not bracketed depict the corresponding propene molecule, while bracketed numbers indicate the position within the molecule.E.g.Cp1(2) is carbon atom 2 in propene molecule 1.