Enhanced Syngas Conversion to Light Aromatics over ZSM-5@boron-modified Silicalite-1 Zeolites Integrated with ZnCrOx

For each sample, the average b-axis length was manually measured for at least 50 well-defined crystals from representative images.N2 adsorption-desorption was carried out on the specific surface area and pore size analyzer (BSD-600M). The sample was firstly degassed at 300 °C in a vacuum for 10 h and then moved to the analysis station for adsorption-desorption at −196 °C. The specific surface area was determined based on the Brunauer-Emmett-Teller (BET) method and the pore volume and pore diameter were calculated based on the Barrett-Joyner-Halenda (BJH) model.X-ray photoelectron spectroscopy (XPS) was collected on a Thermo Scientific K-Alpha with Al Kα at 150 W (hν = 1486.6 eV) under 5 × 10–7 Pa, calibrated internally by the carbon deposit C1s (Eb = 284.8 eV).27Al MAS NMR experiments were tested on Bruker AVANCE III 600 spectrometers with a MAS probe at a spinning rate of 10 kHz at 130.32 MHz. 1.0 M Al(NO3)3 solution was referenced to the chemical shift of 27Al.NH3 temperature-programmed desorption (NH3-TPD) experiments were recorded with a thermal conductivity detector (TCD).

Typically, 100 mg sample was pretreated in an Ar flow (30 mL·min–1) at 400 °C for 1 h. After cooling to 100 °C, the sample was saturated with ammonia flow for 0.5 h, and then the Ar flow was introduced as the sweep gas. Finally, NH3-TPD was presented in the temperature range from 100 to 500 °C at a rate of 10 °C/minThe H2-D2 exchange experiments were carried out on the Micromeritics Autochem 2920 connected to MS.

Firstly, 100 mg of sample was loaded into a quartz tube and processed in a 30 mL·min–1 Ar atmosphere at 350 °C with the rate of 5 °C·min–1 for 1 h. After the temperature was lowered to 50 °C, the sample was cut to a H2/D2 mixture at a flow rate of 30 mL·min–1, and the test was initiated after the baseline was stable. During the test, the temperature was increased to 500 °C at 5 °C·min–1.CO temperature-programmed desorption (CO-TPD) was performed on a Micromeritics Autochem 2920 instrument.

The 100 mg catalyst was pretreated in an Ar flow (30 mL·min–1) at 350 °C for 1 h and then cooled to 50 °C. Then, after adsorbing CO for 30 min, physically adsorbed CO2 on the catalyst surface was purged with an Ar flow of 30 mL min−1. After baseline stabilization, the catalyst was heated from 50 to 750 °C at a rate of 10 °C min−1.Pyridine absorbed infrared (Py-IR) spectroscopy was recorded on a Thermo Scientific (Nicolet 380) spectrometer instrument equipped with an MCT detector.

The sample was placed in a thermostated cell with CaF2 windows and evacuated to 10–2 Pa at 450 °C for 2 h. Then, pyridine vapor was introduced and saturated the sample for 1 h. The Py-IR desorption spectrum was recorded at 150 and 350 °C.In situ Diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments were tested on a Nicolet 6700 instrument equipped with an MCT detector.

In situ absorbance spectra were obtained by collecting 32 scans at 8 cm–1 resolution. Before DRIFTS analyses, the catalysts undergone the same pretreatment in Ar atmosphere at 350 °C for 1 h, which was then cooled down to the target temperatures under Ar and the corresponding background spectra were collected for subsequent DRIFTS analyses. Then, the sample was exposed to a reaction gas (H2/CO = 1, 10 mL min–1).

Subsequently, the spectra were recorded at set intervals.