Confined dual Lewis acid centers for selective cascade C–C coupling and deoxygenation

The selective formation of C–C bonds, coupled with effective removal of oxygen, plays a crucial role in the process of upgrading biomass-derived oxygenates into fuels and chemicals. However, co-feeding reactants with water is sometimes necessary to assist binding sites in catalytic reactions, thereby achieving desirable performance. Here, we report the design of a CeSnBeta catalyst featuring dual Lewis acidic sites for the efficient production of isobutene from acetone via C–C coupling followed by deoxygenation. By incorporating Ce species onto SnBeta, which was synthesized through liquid-phase grafting of dealuminated Beta, we created confined dual Lewis acidic centers within Beta zeolites. The cooperative action of Ce species and framework Sn sites within this confined environment enabled selective catalysis of the acetone-to-isobutene cascade reactions, showcasing enhanced stability even without the presence of water.

The ammonium form of the BEA samples was transformed to the proton form (H-BEA) by calcination at 823 K for 24 h.The dealuminated BEA (Beta-deAl) was synthesized via dealuminating H-BEA by stirring it in a 13 M aqueous nitric acid solution at 373 K for 12 h (100 mL g -1 zeolite).The powder was then filtered, rinsed thoroughly with water (until pH≈7) and dried at 333 K.
SnBeta was synthesized by a liquid phase grafting method. [14]Before the grafting of tin, the powder was activated overnight at 423 K to remove physisorbed water.Next, the sample was suspended in isopropanol (50 mL per gram) and 27 mmol of SnCl4•5H2O per gram of support was added.The solution was refluxed under N2 for 7 hours and afterwards filtered, rinsed first with isopropanol then with ethanol (until pH≈7) and dried at 333 K.The calcination procedure was as follows: ramping 3 K/min to 473 K, dwell for 6 hours, ramping 3 K/min to 823 K and dwell for 6 hours.
The sodium titrated NaBeta-deAl and NaSnBeta was obtained via an ion exchange method.The Beta-deAl or SnBeta was suspended in a 1 M NaNO3 solution (water, 50 mL g -1 material) and the mixture was vigorously stirred at 353 K overnight.The sample was recovered by filtration followed by another time of ion exchange using the same procedure.The materials were then washed thoroughly with water (e.g., 1.5 L per gram material), filtered, and calcined at 823 K for 5 hours (5 K/min).
Cerium was introduced by a wetness impregnation method.A Ce(NO3)3 solution was added to Beta-deAl, SnBeta, NaBeta-deAl, and NaSnBeta to achieve certain weight percentage of Ce (x%) and named as xCeBeta-deAl, xCeSnBeta, xCeNaBeta-deAl, and xCeNaSnBeta.The mixture was then dried at room temperature overnight, at 378 K for 4 hours, and calcined at 823 K for 5 hours (5 K/min).2%Ce/SiO2, and 2%0.4%Sn/SiO2 were synthesized by wetness impregnation method described above.SnMFI and SnSBA-15 were synthesized according to previous reports, 30 the same procedure described above was used for the incorporation of Ce.

Catalyst Characterization
Nitrogen Sorption.Surface area and pore volume of the catalysts were determined DR UV-Vis Measurements.Diffuse Reflectance Ultraviolet-Visible Spectroscopy (DR UV-Vis) reflectance from 200 nm to 800 nm was measured on an Agilent Cary 5000 UV-Vis-NIR spectrophotometer with diffuse reflection accessory.A powder cell containing a thin layer of sample was mounted to the reflectance port.Reflectance (R) of a sample is made relative to the reference material, barium sulfate (BaSO4), which was used to establish the 100% R baseline.The 0% R baseline was obtained by removing the powder cell from reflectance port and allowing the light to be trapped by the sample compartment.
The absorbance (A) was calculated using A=-logR.

DRIFTS Measurements. Diffuse Reflectance Infrared Fourier Transform
Spectroscopy (DRIFTS) -Pyridine and CD3CN were performed with a Bruker Tenser 27 FTIR.About 20 mg catalyst was loaded into the Praying Mantis in situ cell.The sample was first treated in 5% Ar/He (50 SCCM) at 723 K for 30 mins to remove surface impurities.
The background was taken using treated sample at 323 K. Pyridine and CD3CN was then introduced into the cell via a bubbler at room temperature.After 10 mins adsorption, 5% Ar/He was flowed (50 SCCM) for 30 mins at the temperature where background was taken to remove surface physisorbed species.The sample was then ramped to a certain desorption temperature at 10 K/min.After 30 mins purging at each desorption temperature, the catalyst was cooled down to 323 K where spectra were scanned.
1 H MAS NMR Measurements.In situ 1 H MAS (magic angle spinning) NMR (nuclear magnetic resonance) spectra were collected with a 300 MHz Varian Inova NMR spectrometer operating at a 1 H Larmor frequency of 299.97 MHz.All catalysts were pretreated in a glass tube under flowing Ar at 400 °C for 2 h, then sealed and moved into a glovebox.A home-made in situ NMR rotor was used to hold the samples.Samples sealed in the rotor were spun at the magic angle at a spinning rate of 4,000 Hz in a commercial 7.5 mm ceramic probe.A single-pulse width of 4 μs, a recycle delay time of 5 s, and an acquisition time of 0.1 s were used to collect 1000 number of scans per spectrum.
Quantitative fit of the SP MAS NMR spectra was conducted in NUTS.Specifically, baseline fitting was employed to eliminate the background signal.Deconvolution of peaks was conducted using mixed Gaussian/Lorentzian line shapes followed by peaks fitting and integration. 27Al MAS NMR Measurements.Quantitative 27 Al single pulse MAS NMR experiments were conducted on a Varian Inova 850 MHz NMR spectrometer operating at a magnetic field of 19.9 T that is equipped with a 3.2 mm pencil-type commercial MAS probe.All the spectra were obtained at 221.41 MHz using a single pulse (SP) sequence at a pulse angle of 45 deg (0.5 µs) and a recycle delay of 1 s.The samples are all fully hydrated because all the sample were exposed to ambient conditions for months before the measurements.The spectra were accumulated between 5000 and 100000 scans at a sample spinning rate of 19 kHz.All spectra are externally referenced to a 1 M Al(NO3)3 aqueous solution (i.e., the 0 ppm position). 31S Measurements.X-ray photoelectron spectroscopy (XPS) analysis was conducted on a ThermoFisher ESCALAB250 instrument (Physical Electronics) with Al Kα irradiation (1486.6 eV) at the pressure of 1.3 × 10−9 mbar.The binding energy values were referenced to the C 1s at 284.4 eV.

Catalytic Activity and Rate Measurements
The conversion of acetone was performed in a fixed-bed stainless steel reactor (i.d. 5 mm).A thermocouple was placed in the middle of the catalyst bed to monitor the temperature.A certain amount (10-100 mg) of catalyst diluted with SiC (500 mg in total) was loaded into the reactor.The catalyst was pretreated at 723 K (ramping in N2 50 SCCM, ramping rate: 10 K/min) in N2 for 0.5 h (50 SCCM) then decreased to reaction temperature (673 K).Acetone was fed to the evaporator via a syringe pump and carried into the reactor by N2.The temperature of evaporator was 393 K to enable the evaporation of acetone.Shimadzu GC-2014 gas chromatograph equipped with HP-Plot Q column (30m, 0.53mm, 40 μm), flame ionization detector (FID) and thermal conductivity detector via nitrogen sorption experiments carried out on a Micromeritics TriStar II 3020 physisorption analyzer.Catalyst samples were degassed at 350 °C for 3 h under vacuum before experiments were carried out at a temperature of −196 °C.XRD Measurements.X-ray diffraction (XRD) patterns were collected with a Rigaku Miniflex 600 apparatus equipped with a Cu Kα radiation (λ = 0.15406 nm).Bragg's angles were between 10° and 90° with a scanning rate at 1.4 deg/min.Inductively Coupled Plasma (ICP) was performed in Galbraith Laboratories.Microscopy Imaging.Transmission electron microscopy imaging was performed on a FEI Titan 80-300 operated at 300 kV.The images were acquired with a High Angle Annular Dark Field Detector in Scanning Transmission Electron mode.The semiconvergence angle was set to 17.8 mrad, and the inner collection angle was set above 54 mrad.Compositional analysis was performed with a JEOL ARM 200 operated at 200 kV.The microscope houses a high-collection angle Silicon Drift Detector SDD (100 mm2).The samples were prepared by dispersing a dry powder on a lacey-carbon coated 200 mesh Cu grids.

(
TCD) was used to analyze all products.Acetone conversion (X), product selectivity (Si), and carbon balance (CB) were calculated as follows:Conversion (X) = (molacetone-in -molacetone-out) /molacetone-in Selectivity species-i (Si) = (molspecies-i • αi) / (molconverted acetone • 3)Carbon balance (CB) = (sum of moles of carbon out /sum of moles of carbon in) • 100% αi represents the number of carbon(s) in the species-i.The steady state results were obtained by taking average of at least 100 mins conversion or selectivity with carbon balance in the range of 100±15%.

Figure S1 .
Figure S1.Acetone conversion over 2CeSnNaBeta was evaluated before and after oxygen treatment by flowing 20 SCCM of air for 20 minutes at 673 K. Comparable activity after regeneration indicates the reusability of the catalyst.

Figure S4 .
Figure S4.Infrared spectroscopy of CDCN3 adsorbed on SnBeta, 2CeSnBeta, and 2CeNaSnBeta.We observed CD3CN adsorbed on closed Sn sites at 2308 cm -1 as well as the peak tail at 2316 cm -1 (resulted from defect open Sn sites) on all samples. 26CD3CN adsorbed on silanol (2272 cm -1 ) was observed on SnBeta and 2CeSnBeta, while CD3CN adsorption on silanol in 2CeNaSnBeta was barely detectable.The broad peak centered around

Table S1 .
BET surface area and micropore volume of synthesized catalysts.