Controlling Chemical Reactions in Confined Environments: Water Dissociation in MOF-74

Abstract

Abstract:The confined porous environment of metal organic frameworks (MOFs) is an attractive system for studying reaction mechanisms. Compared to flat oxide surfaces, MOFs have the key advantage that they exhibit a well-defined structure and present significantly fewer challenges in experimental characterization. As an example of an important reaction, we study here the dissociation of water-which plays a critical role in biology, chemistry, and materials science-in MOFs and show how the knowledge of the structure in this confined environment allows for an unprecedented level of understanding and control. In particular, combining in-situ infrared spectroscopy and first-principles calculations, we show that the water dissociation reaction can be selectively controlled inside Zn-MOF-74 by alcohol, through both chemical and physical interactions. Methanol is observed to speed up water dissociation by 25% to 100%, depending on the alcohol partial pressure. On the other hand, co-adsorption of isopropanol reduces the speed of the water reaction, due mostly to steric interactions. In addition, we also investigate the stability of the product state after the water dissociation has occurred and find that the presence of additional water significantly stabilizes the dissociated state. Our results show that precise control of reactions within nano-porous materials is possible, opening the way for advances in fields ranging from catalysis to electrochemistry and sensors.

Stabilized open metal sites in bimetallic metal–organic framework catalysts for hydrogen production from alcohols

“…This behavior is consistent with prior observations of methanol adsorption in MOF-74 frameworks. 51,75 In all cases, the lowest energy conguration for methanol was found to be binding via the oxygen atom. The cluster model was also used to predict the energetics of CO binding at the OMS, which is also predicted to be exoergic, regardless of whether the CO is bound via carbon or oxygen (Table S6 †).…”

Insight into the Methylation of Alkenes and Aromatics with Methanol over Zeolite Catalysts by Linear Scaling Relations

“…Similar investigations have been also performed in zeolite catalysis. − Raybaud and co-workers established a BEP relationship to estimate the transition states and to predict the initial dealumination sites in zeolites . For the methylation of HCP intermediates, Studt and co-workers reported that the ammonia adsorption enthalpy could be a descriptor for the activity of Brønsted acid sites in the methylation of alkenes in zeolites with different isomorphically substituted metal ions. , In addition to acid strength, the confinement effect of topology, which reflects the stabilizing or repulsive interaction between the reaction intermediates/transition states and zeolite framework, also showed a significant influence on the activity of the zeolite catalyst …”

“…33,34 In addition to acid strength, the confinement effect of topology, which reflects the stabilizing or repulsive interaction between the reaction intermediates/transition states and zeolite framework, also showed a significant influence on the activity of the zeolite catalyst. 35 Assuredly, the activity of a zeolite catalyst in the methylation of alkenes and aromatics depends on the topology structure and the acidity; a better understanding of the structure−activity relationship is of benefit to screening for improved catalyst materials and further enhancing the efficiency of current MTH processes. In this work, therefore, the methylation of alkene and aromatic HCP intermediates with methanol was investigated across zeolites of multiple topologies including H-SAPO-34, H-BEA, H-ZSM-5, H-ZSM-22, H-ITQ-13, H-MCM-22, H-FAU, and H-ZSM-12 through DFT and microkinetic calculations.…”

Power of Infrared and Raman Spectroscopies to Characterize Metal-Organic Frameworks and Investigate Their Interaction with Guest Molecules

“…At low pressure bands at 3658 and 3575 cm –1 are formed and above 0.1 bar these bands disappear and bands due to H-bonded water (3330, 3220, and 1640 cm –1 ) develop. It was suggested that water dissociates on CPO-27­(Zn) but the process cannot be directly followed by IR spectroscopy because of the bands superimposition. , However, the process was monitored by following the adsorption of deuterated water; a sharp band at 970 cm –1 developed and was assigned to O–D bending vibrations in the linker. The band intensified after evacuation at 473 K.…”