Catalysis by framework zinc in silica-based molecular sieves† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc03889h

Adjustable Zn Lewis acid site distributions in crystalline, microporous zincosilicates were studied spectroscopically and explored for catalytic applications.


CIT-6
CIT-6-LiEx CIT-6-Z0 CIT-6 reZn-pH=6.9 VPI-8 Zn-MCM-41 Zn-MFI SSZ-33 reZn-pH=6.9 SiO 2 reZn-pH=6.9 2311 2290 2280 Fig. S3: Normalized powder XRD data for selected microporous materials (from top to bottom): Zr-Beta, CIT-6, CIT-6-reZn-pH=6.9, VPI-8, Zn-MFI, and SSZ-33-reZn-pH=6.9. All materials have been calcined. XRD pattern of the parent CIT-6 sample does not have noticeable VPI-8 peaks, but, upon 1M H 2 SO 4 treatment, Zn-reinsertion, and calcination, a shoulder in the low angle peak of *BEA becomes apparent, indicating the presence of VPI-8 (VET framework) as a minor phase impurity. Crystal aggregates of VPI-8 morphology are also observed among *BEA crystals. The increase in the prominence of the VET peak in the powder pattern may be associated with selective partial degradation of the *BEA framework in the treatment of the sample, as it is a less dense structure. ZnO CD 2 CNand polyanions Scheme S1: Illustration of glucose isomerization mechanisms promoted by bases and Lewis acids. For reactions performed in deuterated solvents (D 2 O or MeOD), deuterium incorporation is expected for products formed through enolate intermediates, but not through intramolecular hydride shifts. The use of 13 C-C1-glucose enables product analysis without the need for fractionation.

Fig. S5:
13 C NMR spectrum of unseparated reactant ( 13 C-C1-glucose) and the products generated by CIT-6 at 100 °C after a 1h reaction in D 2 O. The abbreviations "pyr" and "fur" stand for pyranose and furanose, respectively. Incorporation of deuterium at C1 position of fructose, as evidence by appearance of low-intensity triplets, indicates a base-catalyzed mechanism. The presence of 1 H-form of fructose likely originates from the small fraction of 1 H impurity in D 2 O solvent, but could also arise from a small contribution from a hydride shift mechanism. Unlabeled peaks correspond to natural abundance 13 C (~1%) occurring in glucose C2-C6 positions.
Step 1 is a Diels-Alder cycloaddition step.
Step 2 is a Lewis acid promoted rearrangement to an epoxide proposed for the dimethyl furan analog of the oxa-norbornene cycloadduct.
Step 3 is a Lewis acid promoted hydride shift that isomerizes the epoxide to the enone. Benzene is hypothesized to form through steps 4 and 5 that are also proposed for the analogous dehydrative-aromatization of dimethyl furan to p-xylene. Intermediates highlighted in red were not detected in this study.

Fig. S11:
Catalyst recycle experiments for Diels-Alder cycloaddition-dehydration reactions of DMFDC catalyzed by CIT-6-re-Zn-pH=6.9 at 210 °C. Run 1 uses as-made CIT-6-re-Zn-pH=6.9; Run 2 uses catalyst recovered after Run 1, triply washed by acetone, and dried; Run 3 uses catalyst recovered after Run 2, triply washed by acetone, and dried; Run 4 uses catalyst recovered after Run 3, triply washed by acetone, dried, and calcined. Resulting yields (%) of DMT, MF, MB, CHO, and DMFDC are calculated as ratio of moles formed to initial moles of DMFDC. Mass on catalyst (%) is expressed as ratio of combustible mass on catalyst (measured by TGA) to initial mass of DMFDC. Reaction conditions: reagent and solvent ratios were adjusted to keep constant ratio to inorganic catalyst content between runs; 35 bar C 2 H 2 at 25 °C, 12h reaction time. Normalized powder XRD data for as-made CIT-6-reZn-pH=6.9 (bottom), and CIT-6-reZn-pH=6.9 recovered after Run 3 in Fig. S11 (top).