Search

Promoting the activity of catalyst, achieving high CO2 conversion and increasing light olefins yield are important in CO2 hydrogenation to olefin. Herein, SiO2 was doped in CuO‐ZnO‐ZrO2 to form multi‐oxides of CuO‐ZnO‐ZrO2‐SiO2 by co‐precipitation method, and the multi‐oxides was mixed with SAPO‐34 molecular sieves mechanically to form a composite catalyst of CuO‐ZnO‐ZrO2‐SiO2/SAPO‐34. Compared with CuO‐ZnO‐ZrO2, doping of SiO2 increases the dispersion and thermal stability of metal oxides, provides more sites for CO2 activated, and delays the aggregation of metal particles at higher temperature. Doped SiO2 can also adsorb the water from hydrogenation process to improve the olefins yield and hinder the formation of CO from reverse water gas shift. Thus, under the condition of reaction temperature at 420 °C, pressure of 3.0 MPa, space velocity of 1800 mL gcat−1 h−1, CO2/H2 (molar ratio) of 1 : 3 and the mass ratio of CuO‐ZnO‐ZrO2‐SiO2 (containing 8 % SiO2) to SAPO‐34 of 1 : 1, the direct CO2 hydrogenation to light olefins on CuO‐ZnO‐ZrO2‐SiO2/SAPO‐34 shows that the conversion of CO2 is 53.9 % and the selectivity of light olefins is 52.9 %, while the CO selectivity is only 13.6 %. [ABSTRACT FROM AUTHOR]

[Display omitted] • The adsorption energies of CO 2 on the surface oxygen vacancies of different crystalline In 2 O 3 were calculated using DFT. • The effect of the spatial distributions of two active components on the CO 2 hydrogenation to aromatics was studied. • The acidity of catalyst under different spatial distributions was studied through NH 3 -TPD. In tandem catalysts, not only good synergy between the two active components is required, but also the precise control of the spatial distribution between the two active components of metal oxides and zeolite is crucial for the migration and conversion of reaction intermediates in the direct conversion of CO 2 to hydrocarbons. The correlation between the metal and the acidic site of zeolite has traditionally been simplified as "the closer, the better". However, it should be noted that this principle only holds true for a portion of tandem catalysts. Therefore, this paper studied the effect of different crystalline In 2 O 3 (cubic phase, hexagonal phase, and mixed cubic/hexagonal phase) and sheet HZSM-5 zeolite tandem catalysts on the activity of CO 2 hydrogenation reaction under different spatial distribution. The generalized gradient approximation (GGA) of density functional theory (DFT) were used to simulate the adsorption energy of CO 2 by oxygen vacancy on c-In 2 O 3 (1 1 1) and h-In 2 O 3 (1 0 4) planes, it was found that O v1 on c-In 2 O 3 (1 1 1) and O v4 on h-In 2 O 3 (1 0 4) had the strongest adsorption energy for CO 2. In addition, it has been observed that the proximity of the two active components (e.g., during mortar mixing) results in decreased catalytic performance. This is due to the migration of metal In, which neutralizes the acid sites of zeolites and leads to inefficient conversion of methanol reaction intermediates to aromatics. As a result, CO 2 conversion and aromatic selectivity are decreased. [ABSTRACT FROM AUTHOR]

We prepared ZnZr 7 O/HZ-1.5NH 4 F tandem catalyst with high catalytic activity for the direct conversion of CO 2 hydrogenation to aromatics by combining theoretical calculations and experiments. [Display omitted] • It was simulated that the (0 1 0) plane of the sheet HZSM-5 had the strongest adsorption capacity for CH 3 O* and CHOO*. • We prepared catalysts with high catalytic activity and stability by combining theoretical calculations and experiments. • The thickness can be precisely adjusted to prepare a series of sheet HZSM-5 by adding urea and NH 4 F. • Urea inhibits the generation of defective sites in HZSM-5, while NH 4 F promotes the generation of defective sites. • The thickness of the sheet HZSM-5 is also a factor affecting the catalytic activity. The adsorption properties of CH 3 O* and CHOO* adsorbed on the three crystal planes (0 0 1, 0 1 0, 1 0 1) of HZSM-5 were simulated by the generalized gradient approximation (GGA) of density functional theory (DFT), it was found that the (0 1 0) plane corresponding to the b-axis of the sheet HZSM-5 had the strongest adsorption energy for CH 3 O* and CHOO*. Therefore, we successfully synthesized sheet HZSM-5 with different thicknesses by adding the inhibitor (urea) and mineralizer (F−) to the synthesis system based on the theoretical calculations. The physicochemical properties of HZSM-5 were investigated by the characterization methods of SEM, TEM, Py-IR, OH-IR, CO 2 -TPD and so on. The results showed the thickness of HZSM-5 can be precisely adjusted by adding urea and NH 4 F and changing the ratio of urea/NH 4 F or TPAOH/NH 4 F. Then, the sheet HZSM-5 and ZnZr 7 O were connected in tandem to investigate the reaction conditions and catalytic performance for the direct conversion of CO 2 hydrogenation to aromatics. It was found that the HZ-1.5NH 4 F had a large specific surface area, suitable B acid content and more defect sites. These advantages resulted in a high aromatic selectivity of 77.5% and CO 2 conversion of 17.6% over ZnZr 7 O/HZ-1.5NH 4 F. Meanwhile, it exhibits stable performance and no significant deactivation after 80 h of operation. [ABSTRACT FROM AUTHOR]

• The H-ZSM-5 with different morphologies were rationally designed and the synthesis mechanism was illustrated. • Physical mixture of H-ZSM-5 and In 2 O 3 , Cu-Zn-Al and ZnZrO were used to CO 2 hydrogenation to aromatics. • The fewer intermediates were observed on the Cu/ZnO/Al 2 O 3 -sheetZ5 and In 2 O 3 -sheetZ5 in In-situ DRIFTS spectra. • The ZnZr 7 O(5 0 0)-sheet-Z5 showed the best catalytic performance of BTX, the high selectivity of p-xylene was achieved over the ZnZr 7 O(5 0 0)-chainZ5. • Enhanced CO 2 conversion by ZnZr 7 O(5 0 0)-sheet-Z5 catalysts at suitable calcination temperature and oxygen vacancy concentration. The efficient that to concert CO 2 into high value-added chemicals is a promising and potential strategy to reduce the consumption of petroleum resources, especially as an alternative route to MTA, where direct conversion of aromatics can be achieved through CO 2 hydrogenation. Herein, a series of metal oxides (In 2 O 3 , Cu-Zn-Al and ZnZr x O with different Zr/Zn and calcined at different temperatures) and different morphologies of spherical, hollow, sheet, and chain HZSM-5 were rationally designed, and then connected with metal oxides and HZSM-5 in tandem to investigate the reaction conditions and catalytic performance for the direct conversion that from CO 2 hydrogenation to aromatics, the reaction mechanism was investigated using In-situ DRIFTS. Furthermore, due to the synergy between the respective excellent properties of HZSM-5 zeolites and metal oxides, the selectivity of aromatic up to 75.7% and conversion of CO 2 was 14.5% over ZnZr 7 O(5 0 0)-sheet HZSM-5 tandem catalyst, while achieving high selectivity of 64.1% for BTX. Moreover, high selectivity of the target product to xylene was achieved over the ZnZr 7 O(5 0 0)-chain HZSM-5 tandem catalyst due to the fact that the molecular kinetic radius of p-xylene was close to the b-axis pore radius of HZSM-5, and an appropriate increase in the b-axis length was beneficial to improve the selectivity of p-xylene, which opened up a broad path for the design of catalysts for CO 2 hydrogenation to aromatics. [ABSTRACT FROM AUTHOR]