Search

Direct conversion of carbon dioxide (CO 2) to high added-value chemicals is available for reducing reliance on fossil fuels and mitigating CO 2 emissions, but both the chemical inertness of CO 2 and the difficulty of carbon chain growth make it difficult to enhance the activity of the catalyst. In this work, we developed a multifunctional catalyst composed of K-promoted spinel structured CoFeOx and HZSM-5 that efficiently converted CO 2 to light-weight hydrocarbons via CO 2 modified Fischer-Tropsch synthesis path (CO 2 -FTS), and the best catalyst exhibited a remarkably efficient CO 2 conversion of 51.2% and liquid hydrocarbons space-time yield (STY) of 3.4 μmol C5+ ·g cat −1·s−1 along with an extremely low selectivity of 5.5% toward undesired CO. By analysis of structural characterizations and reaction results, the noticeable performance of the multifunctional catalyst critically lies in the beneficial interaction between Co and Fe, the promoting effect of potassium, and the concertedly synergistic effect between K-CoFeOx and HZSM-5. In situ XRD, XPS, and TPD characterizations further indicate that the introduction of cobalt promotes the reduction of iron by forming a Fe0-rich FeCo alloy, which is beneficial for the adsorption of intermediate CO and facilitates the in situ generation of active iron carbide. K as an electronic promoter is added to increase the surface basicity, enhance the adsorption of CO 2 and weaken the adsorption of H 2 , which favor CO 2 conversion and carbon chain growth. Additionally, through passivation of the strong acidic site of HZSM-5 by Si treatment and varying the mixing mode of HZSM-5 and nK-CoFeOx, the synergistic effect of the two components promotes CO 2 conversion and noteworthily increases the distribution of light-weight hydrocarbons, especially benzene, toluene, and xylene on composite catalyst by aromatization over active sites with appropriate acidity and proximity. This study provides valuable guidelines for designing selective and efficient iron-based composite catalysts to obtain value-added FTS products and light aromatics. [Display omitted] • Fe-Co interaction promotes the adsorption and dissociation of CO intermediates and carburization of iron species. • The addition of K enhances CO 2 adsorption and weakens H 2 adsorption. • The synergy of different active sites is crucialin the tandem catalysis process. • Passivating zeolite acidity by Si treatment promotes the selectivity of liquid hydrocarbons. • 5 K-CoFeOx(1:5)/HZSM-5 exhibits exceptional high liquid hydrocarbons space-time yield at 51.2% CO 2 conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The crystalline phases of ZrO 2 greatly influence the catalytic performance over Pd/In 2 O 3 catalysts. • Pd/In 2 O 3 /Mix-ZrO 2 catalyst with mixed ZrO 2 phases exhibits a high STY of methanol. • The large size of Pd nanoparticles favors H 2 dissociation and CO 2 /intermediates hydrogenation. • The number of medium basic sites and oxygen vacancies are vital for superior performance. The crystalline phases of support have great influence on their surface and structure properties. Therefore, adjusting the crystalline structure of heterogeneous catalysts imposes a significant impact on the catalytic performance. Herein, a suite of Pd/In 2 O 3 /ZrO 2 catalysts with different crystalline phases of ZrO 2 were prepared and evaluated for CO 2 hydrogenation to CH 3 OH using the same amount of metal loading. The activity data showed the distinct superior reactivity of Pd/In 2 O 3 /ZrO 2 catalyst used mixed monoclinic and tetragonal phases ZrO 2 (Mix-ZrO 2) as support as compared to respective single phase of monoclinic ZrO 2 (m-ZrO 2) and tetragonal ZrO 2 (t-ZrO 2). The catalysts are extensively characterized through BET, XRD, HRTEM, UV–vis, H 2 -TPR, CO 2 /H 2 -TPD and XPS. Combining the characterization results and activity data, the superior activity of Pd/In 2 O 3 /Mix-ZrO 2 catalyst can be correlated with large particle size of Pd nanoparticles, the concentration of oxygen vacancies, and the abundant medium basic sites, which were essential for activation of H 2 and inert CO 2 and enhancement of catalytic performance. The best-performing Pd/In 2 O 3 /Mix-ZrO 2 catalyst exhibited a remarkable reactivity with space time yield (STY) of 0.54 g methanol ·h−1·g cat −1 at 573 K and 5 MPa, and stability without noticeable deactivation after 100 h of time on stream, demonstrating its potential as catalyst used in CH 3 OH synthesis from CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]

Advances in design concept of oxide-zeolite (OX-ZEO) bifunctional tandem catalysts have demonstrated its potential for highly enhanced selectivity and yield in CO 2 conversion by assigning CO 2 activation and C-C coupling to specific oxide and zeolite, respectively. However, the crystalline structural effects of oxides have not been thoroughly investigated. Here, ZnO/ZrO 2 with different ZrO 2 crystalline phases modulated by Li doping has been used as an oxide catalyst to combine with SAPO-34 as a bifunctional composite catalyst for CO 2 hydrogenation to light olefins. With the transformation of the support ZrO 2 crystalline phase from tetragonal phase to mixed crystalline phase in the catalyst, the CO 2 conversion and yield of target product light olefins were significantly improved. The best-performing ZnO/5Li-ZrO 2 catalyst exhibited a CO 2 conversion of 28.56%, light olefins selectivity of 82.00% with a yield of 8.77% along with good stability under the reaction conditions of 380 °C, 3 MPa, and 6000 mL/g/h. The characterization results by XRD, Raman, HRTEM, XPS and CO 2 -TPD confirmed that the highly enhanced catalytic performance was attributed to the strong interaction between the mixed crystal phase 5Li-ZrO 2 and ZnO, which generated a large number of oxygen vacancies for CO 2 activation. The results indicate that controlling the crystal phase of the oxide support is of prime importance in designing more active and selective oxide-zeolite bifunctional catalysts for high-efficiency CO 2 to light olefins conversion. [Display omitted] • The mixed ZrO 2 crystal phases boost the catalytic hydrogenation of the bifunctional tandem catalysts. • The ZnO/5Li-ZrO 2 -SAPO-34 tandem catalysts exhibits superior activity due to strong interaction between ZnO and 5Li-ZrO 2. • The ZnO/5Li-ZrO 2 catalysts possess a large number of oxygen vacancies and moderately basic sites. • The ZnO/5Li-ZrO 2 -SAPO-34 tandem catalysts exhibits high CO 2 conversion (28.56%) and light olefins yield (8.77%) at 380 °C. [ABSTRACT FROM AUTHOR]