Polyoxymethylene dimethyl ethers (PODE n ) converted from methanol and formaldehyde were investigated with alumina supported ZrO2 catalyst in a stainless steel tube fixed-bed reactor within the temperature range from 333 to 433 K and the pressure range from 0.1 to 2.5 MPa. First, results from catalytic performance tests showed that the catalyst γ-Al2O3 containing 4 mol % ZrO2 exhibited the highest activity for PODE n synthesis. The stoichiometry analysis of raw material indicated that ZrO2 modified catalyst had the optimum activity at methanol/formaldehyde = 3 (mol/mol). An increase of the reaction pressure resulted in a significant increase in methanol conversion from 13.18 to 48.64%, and selectivity to PODE3–8 was enhanced to 24.82%. The temperature experiment analysis confirmed the optimization of the reaction temperature to be 393 K. Second, SEM and TEM showed the relationship between the catalytic activity and the catalyst-crystal alignment. Incorporation of ZrO2 in the framework of γ-Al2O3 was noticed and confirmed by X-ray diffraction (XRD) and BET analysis. The NH3-TPD tests indicated the relationship between catalytic activity and acidity. Finally, an elimination mechanism was proposed to explain the PODE n synthesis reaction rate and kinetic model. The contributions of intraparticle and external diffusion were eliminated by changing the size of catalyst particles and space velocity. The proposed model can reasonably predict the observed behaviors of PODE n synthesis from methanol and formaldehyde.

Direct hydrogenation of carbon dioxide (CO2) to value-added chemicals is a promising strategy to relive the greenhouse effect and replace the diminishing fossil fuels, but the huge CO2 inertness and C–C coupling barrier usually bring about numerous difficulties and count against catalytic performance. Here, a highly active and more economical composite catalyst composed of Cu-promoted Fe2O3 (nCu-Fe2O3) and HZSM-5 was developed for the selective conversion of CO2 to aromatics with 56.61% selectivity at a single pass. An extremely low CO selectivity of 3.51 at 57.30% CO2 conversion outperforming the previously reported conversion was achieved because of the beneficial synergism between Cu and Fe and the distinctive CO reduction prior to reaction which is favorable to the formation of oxygen vacancies for CO2 adsorption and iron carbide for Fischer–Tropsch synthesis (FTS). Additionally, through integrating HZSM-5 synthesized by the phase-transfer method (HZSM-5-pt) with nCu-Fe2O3, the distribution of benzene, toluene, and xylene in aromatics can be noteworthily increased to 54.18% and aromatics selectivity can be increased to 61.94%, without depression of catalyst activity. More significantly, a “H recycling” mechanism was found between oxide and zeolite, which plays a crucial role in “the disposal of H” within dehydrogenative aromatization, facilitating the formation of aromatics. In summary, nCu-Fe2O3/HZSM-5 demonstrates a prospective industrial application in aromatics production from CO2.

The conversion of syngas to aromatics over composite catalysts, comprising a mixture of Fe2O3-SiO2 and Nb-/Ni- modified HZSM-5 (HZ), CuO-ZnO-Al2O3 (CZA) and Nb-/Ni- modified HZ, and a mixture of above two kinds of metal oxides and Ni-HZ, were investigated at 330 °C, 4 MPa and H2:CO = 2:1. Catalysts were characterized to analyze the properties. Fe2O3-SiO2/modified-HZ had the high selectivity of BTX, while CuO-ZnO-Al2O3/modified-HZ had the high selectivity of durene. Fe-CZA/Ni-HZ exhibited higher selectivity of trimethylbenzene (triMB) than both Fe/Ni-HZ and CZA/Ni-HZ, lower selectivity of BTX and tetramethylbenzene (tetraMB), compared with Fe/Ni-HZ and CZA/Ni-HZ, respectively. Reaction pathways were speculated to illustrate the diverse distribution of aromatics. The incorporation of Nb and Ni on the parent HZSM-5 increased the selectivity of aromatics due to their various acidity. The highest selectivity of BTX was obtained over Fe/Ni-HZ and the highest selectivity of durene was achieved over CZA/Nb-Ni-HZ.