One-pass selective conversion of syngas to para-xylene

We presented a promising hybrid catalyst, named Cr/Zn–Zn/Z5@S1, to effectively realize the one-pass selective conversion of syngas to para-xylene.


Table of Contents
Experimental section S3-7

S5
The crystal structures of catalysts were determined by powder X-ray diffraction patterns (XRD), which were performed at Rigaku RINT 2400 X-ray Diffractometer equipped with a Cu Kα radiation. Scans were recorded in the 2θ range 5-90° with a step size of 0.02 °/s. The physical properties of catalysts, such as surface area, microspore volume and average pore size, were analyzed by N 2 physical adsorption at 77 K. These data were measured using Micrsmertics 3Flex specific surface area and porous physical adsorption analyzer. All samples were degassed in vacuum at 473 K for 5 h before measurement. The X-ray photoelectron spectroscopy (XPS) analysis was done by Thermo Fisher Scientific ESCALAB 250Xi multifunctional X-ray photoelectron spectroscope, by which to determine the existence of Al and Zn on the outward appearance of catalysts.
The data processing was performed using Avantage software. The inductive coupled plasma atomic emission spectrometry (ICP-AES) was employed to determine the real Zn content of zeolite materials using Perkin Elmer Optima 7300DV atomic emission spectrometry spectrometer.
NH 3 temperature programmed desorption (NH 3 -TPD) was conducted by a catalyst analyzer BELCAT-B-TT (BEL Japan Co. Ltd.) equipped with a thermal conductivity detector (TCD). 0.03 g sample was pretreated at 423 K in He flow for 1 h, then 5% NH 3 in He was introduced for 1 h with flow rate of 20 ml/min while temperature was cooling down to 353 K. Subsequently, the microreactor was purified with pure He for 1 h. Finally, the NH 3 desorption procedure was proceeded in He flow (30 ml/min) by increasing the temperature from room temperature to 1073 K with a ramping rate of 5 K/min. The density of acid sites was quantified by peak area of the high-temperature NH 3 -desorption peaks.

S6
H 2 temperature programmed reduction (H 2 -TPR) profiles of the samples were tested by a catalyst analyzer BELCAT-B-TT (BEL Japan Co. Ltd.) with a thermal conductivity detector (TCD). Cr/Zn catalysts (0.030 g) were pretreated at 423 K in He flow for 1 h, followed by temperature programmed reduction in H 2 with flow rate of 30 ml/min from room temperature to 1173 K with a ramping rate of 10 K/min. Thermogravimetry (TG) measurement was carried out over 10 mg spent catalysts in air with flow rate of 30 ml/min using TA-60WS thermal analyzer (Shimadzu). The program was performed at the heating rate of 10 K/min from room temperature to 1173 K.

Catalysts evaluation for para-xylene (PX) direct synthesis from syngas
The catalyst performance evaluation of catalysts for PX direct synthesis from syngas was carried out in a fixed-bed steel reactor with internal diameter of 6 mm. All of catalysts were first reduced in the reactor for 10 h at 673 K with pure H 2 . After cooling down to the room temperature, syngas with H 2 /CO molar ratio of 2 was introduced into the reactor. Then, the reaction was conducted at 673 K under 5.0 MPa.
All the products were kept in the gas phase from reactor to outlet and analyzed by an on-line gas chromatograph (GC-8A, Shimadzu), which was equipped with Plot S columns for the thermal conductivity detector (TCD), and HP-PLOT/Q columns for the flame ionization detector (FID). The CO conversion and the hydrocarbons selectivity were calculated with the followed equations, using Ar as an inner standard.

Figures and Tables
Scheme S1 Illustration on the synthesis of the Zn/Z5 and the typical core-shellstructured Z5@S1 and Zn/Z5@S1 zeolite with Z5 (Si/Al=46) as based zeolite.
The XRD profiles of all the zeolite components used for hybrid catalyst preparation are shown in Figure S1.   Figure S3. The primary spectra of Zn 2p, Cr 2p, O 1s and C 1s were obtained from the XPS survey of Cr/Zn oxides ( Figure S3a). Moreover, the ratio of Cr/Zn was 2.08 from XPS, which was in agreement with XRD and EDS results. Binding Energy (eV)
The reducibility of Cr/Zn catalyst was evaluated by H 2 -TPR and the profile was shown in Figure S4. The Cr/Zn catalyst presented one main hydrogen consumption peak located in the range of 500-673 K. S13 Figure S5. SEM images of a) Z5, b) Z5@S1, c) Zn/Z5 and d) Zn/Z5@S1 materials.
We employed SEM to characterize all the zeolite catalysts and the results were shown in Figure S5. S14 Figure S6.  The textural properties of different catalysts were measured by nitrogen physical adsorption. The nitrogen adsorption-desorption isotherms of different catalysts were shown in Figure S7. The corresponding physical properties, BET surface area, pore volume and size, were listed in the followed Table S2. The acidity properties of the zeolite components used for hybrid catalysts preparation were evaluated by NH 3 -TPD, and the results were shown in Figure S8 and Si/Al=750 Si/Al=82 Si/Al=46 Intensity (a.u.)
The NH 3 -TPD profiles of H-ZSM-5 with different Si/Al ratio were displayed in the Figure S9. The NH 3 desorption peak areas of weak and strong acid sites decreased with increasing the Si/Al ratio. It was consistent with the acidic sites from the calculation, as presented in Table S5.   TG was applied to measure the deposited coke on the spent hybrid catalysts. The analysis results of the spent catalysts after 10 h reaction time were compared in Figure   S12. As presented in Table S2, Cr/Zn catalysts illustrated BET surface area of 98.9 m 2 /g, pore volume of 0.58 cm 3 /g and 21.5 nm averaged pore size. The BET surface area, pore volume and average pore size of hybrid catalysts were similar because of the same ratio of Cr/Zn and approximate textural properties of Z5-based zeolite materials. Others mainly consisted of ethene and propene.

S23
We prepared a series of hybrid catalysts Cr/Zn-Z5 with the Z5 zeolite that has varied Si/Al ratio as zeolite component. We investigated their catalytic performance for one-pass PX synthesis from syngas. The reaction results were shown in Table S5. The CO conversion decreased slightly with increasing the Si/Al ratio of Z5. It seems that the Z5 zeolite with Si/Al ratio of 46 was more suitable for PX synthesis over the hybrid catalyst. Therefore, other hybrid catalysts were prepared by mixing Cr/Zn and the Z5 (Si/Al=46) derived zeolite components. Others mainly consisted of ethene and propene.

S26
The Cr/Zn catalyst and all hybrid catalysts were evaluated to realize the PX direct synthesis from syngas and the reaction results were shown in Table S6. The Cr/Zn-Zn/Z5@S1 hybrid catalyst presented excellent para-xylene selectivity of 27.6% with CO conversion of 55.0%. xylene=OX, meta-xylene=MX, para-xylene=PX, C 6 -C 8 are the aromatics except for xylene. c Others mainly consisted of ethene and propene.

S27
We prepared a series of hybrid catalysts Cr/Zn-Zn/Z5@S1 with different weight ratios of Cr/Zn and Zn/Z5@S1. We investigated their catalytic performance for one-pass PX synthesis from syngas. The reaction results were shown in Table S7. The CO conversion decreased slightly with increasing the Zn/Z5@S1 amount. Moreover, the Cr/Zn-Zn/Z5@S1-2/1 realized the highest PX selectivity of 27.6%. It confirmed that the Cr/Zn zeolite with Zn/Z5@S1 ratio of 2 was more suitable for PX synthesis over the hybrid catalyst.