N/S-Heterocyclic Contaminant Removal from Fuels by the Mesoporous Metal–Organic Framework MIL-100: The Role of the Metal Ion

The influence of the metal ion in the mesoporous metal trimesate MIL-100­(Al³⁺, Cr³⁺, Fe³⁺, V³⁺) on the adsorptive removal of N/S-heterocyclic molecules from fuels has been investigated by combining isotherms for adsorption from a model fuel solution with microcalorimetric and IR spectroscopic characterizations. The results show a clear influence of the different metals (Al, Fe, Cr, V) on the affinity for the heterocyclic compounds, on the integral adsorption enthalpies, and on the uptake capacities. Among several factors, the availability of coordinatively unsaturated sites and the presence of basic sites next to the coordinative vacancies are important factors contributing to the observed affinity differences for N-heterocyclic compounds. These trends were deduced from IR spectroscopic observation of adsorbed indole molecules, which can be chemisorbed coordinatively or by formation of hydrogen bonded species. On the basis of our results we are able to propose an optimized adsorbent for the deep and selective removal of nitrogen contaminants out of fuel feeds, namely MIL-100­(V)

N/S-Heterocyclic Contaminant Removal from Fuels by the Mesoporous Metal–Organic Framework MIL-100: The Role of the Metal Ion

The influence of the metal ion in the mesoporous metal trimesate MIL-100­(Al³⁺, Cr³⁺, Fe³⁺, V³⁺) on the adsorptive removal of N/S-heterocyclic molecules from fuels has been investigated by combining isotherms for adsorption from a model fuel solution with microcalorimetric and IR spectroscopic characterizations. The results show a clear influence of the different metals (Al, Fe, Cr, V) on the affinity for the heterocyclic compounds, on the integral adsorption enthalpies, and on the uptake capacities. Among several factors, the availability of coordinatively unsaturated sites and the presence of basic sites next to the coordinative vacancies are important factors contributing to the observed affinity differences for N-heterocyclic compounds. These trends were deduced from IR spectroscopic observation of adsorbed indole molecules, which can be chemisorbed coordinatively or by formation of hydrogen bonded species. On the basis of our results we are able to propose an optimized adsorbent for the deep and selective removal of nitrogen contaminants out of fuel feeds, namely MIL-100­(V)

<i>p</i>-Xylene-Selective Metal–Organic Frameworks: A Case of Topology-Directed Selectivity

Para-disubstituted alkylaromatics such as <i>p</i>-xylene are preferentially adsorbed from an isomer mixture on three isostructural metal–organic frameworks: MIL-125(Ti) ([Ti₈O₈(OH)₄(BDC)₆]), MIL-125(Ti)-NH₂ ([Ti₈O₈(OH)₄(BDC-NH₂)₆]), and CAU-1(Al)-NH₂ ([Al₈(OH)₄(OCH₃)₈(BDC-NH₂)₆]) (BDC = 1,4-benzenedicarboxylate). Their unique structure contains octahedral cages, which can separate molecules on the basis of differences in packing and interaction with the pore walls, as well as smaller tetrahedral cages, which are capable of separating molecules by molecular sieving. These experimental data are in line with predictions by molecular simulations. Additional adsorption and microcalorimetric experiments provide insight in the complementary role of the two cage types in providing the para selectivity