A van der Waals (vdW) corrected density functional theory (DFT) study of the methanol-to-DME reaction on H-ZSM-5 is conducted for both the associative and dissociative pathways. Calculations are performed for four different active site locations corresponding to Al sitings in sinusoidal and straight channels, and their intersections in the MFI zeolite framework. The Gibbs free energy landscape along the reaction paths computed for a typical set of conditions shows that the associative route is preferred, regardless of Al siting, but a transition in the mechanism from associative to dissociative is observed at higher temperatures. The crossover temperature, however, is not identical for the various active site locations, resulting in a temperature range over which both mechanisms are active. This observation may explain why methoxy, which is the key intermediate along the dissociative pathway, has been observed spectroscopically, whereas kinetic analysis points to dominant contributions of the associative pathway under similar conditions. Pore confinement effects largely contribute to transition state stabilization and have a significant impact on the reaction mechanism. The effect of acidity on kinetic performance is also tested by the substitution of three different heteroatom dopants (Al, Ga, In) at the active sites, but only a minor transition-state energy variation was observed. The fundamental information obtained in this study contributes to a better understanding of the complex interplay between pore confinement, acidity, and reaction conditions, and their effect on pathway selectivity. This knowledge can be utilized to either optimize DME production from methanol or facilitate the production of desired hydrocarbons in the methanol-to-hydrocarbon (MTH) process, which requires DME formation to initiate the conversion.

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The design of materials with spatially controlled chemical composition has potential advantages for wide-reaching applications that span energy to medicine. Here, we present a method for preparing a core-shell aluminosilicate zeolite with continuous translational symmetry of nanopores and an epitaxial shell of tunable thickness that passivates Brønsted acid sites associated with framework Al on exterior surfaces. For this study, we selected the commercially relevant MFI framework type and prepared core-shell particles consisting of an aluminosilicate core (ZSM-5) and a siliceous shell (silicalite-1). Transmission electron microscopy and gas adsorption studies confirmed that silicalite-1 forms an epitaxial layer on ZSM-5 crystals without blocking pore openings. Scanning electron microscopy and dynamic light scattering were used in combination to confirm that the shell thickness can be tailored with nanometer resolution (e.g., 5-20 nm). X-ray photoelectron spectroscopy and temperature-programmed desorption measurements revealed the presence of a siliceous shell, while probe reactions using molecules that were either too large or adequately sized to access MFI pores confirmed the uniform shell coverage. The synthesis of ZSM-5@silicalite-1 offers a pathway for tailoring the physicochemical properties of MFI-type materials, notably in the area of catalysis, where surface passivation can enhance product selectivity without sacrificing catalyst activity. The method described herein may prove to be a general platform for zeolite core-shell design with potentially broader applicability to other porous materials.

What is the most significant result of this study?In this study,w ed iscovered that subtle differences in crystal polymorph structure can have ap rofound influence on material properties. The remarkable aspect of the two polymorphs in this particular study-GIS types P1 and P2-is the fact that their topology is nearly identical, yet as light rotation in the framework along with the replacement of one aluminum atom in the unit cell with as ilicon atom is sufficient to change the thermal stability of the material by more than af actor of two. This unexpected result could potentially impact the design of zeolites for ah ost of applications requiring (hydro)thermally robust isostructures. What was the inspiration for this cover design?When designing the cover,w ew anted to accomplish two objectives. The first was to highlight the hierarchical nature of our collaborative research that spanned multiple length scales:t hat is, from macroscopic adsorption studies and microscopic materials characterization to atomistic modeling. The cover image highlights bulk sorbents that can be used for separations, am icroscopic image of az eolite crystal framework, and an individual pore operating as as ize-exclusion sieve. As econd aspect that we wanted to emphasize was the relevance of our findings to applications in the energy and chemicals industries. In our study,w eu sed ac ommercially viable approach to prepare GIS-type zeolites. To this end, their performance as selective sorbents may prove beneficial for expanding this work beyond the benchtop to be of practical use in industrial separations or adsorption technologies. What other topics are you working on at the moment?The research programs of the three principal investigatorsGrabow,M otkuri, and Rimer-all fall under the general umbrella of nanoporous materials. Each of us studies zeolites, but for different applications-Grabow and Rimer focus on catalysis, whereas Motkuri, in addition to zeolites, is also interested on metal-organic frameworks for their sorption/separation applications. We are continuing to investigate aw ide range of open framework materials for these applications. An underlying theme of our work is the elucidation of structure-performance relationships, and the design of novel pathways to generate new/improved materials in pursuit of advancing these fields of research beyond current state-of-the-art technologies.Invited for the cover of this issue are the groups of R. K. Motkuri and J. D. Rimer at the Pacific Northwest National Laboratory and University of Houston, respectively.T he image depicts bulk sorbents that can be used for separations, am icroscopic image of az eolite crystal framework,a nd an individualp ore operating as as ize-exclusion sieve. Read the full text of the ar-

Here, we discuss the fabrication of oriented films of UiO-66 crystals via the solution shearing based deposition of the crystal suspension over functionalized silicon substrates.