On the intimacy of bifunctional catalysts for the conversion of syngas to light olefins - Archive ouverte HAL
Communication Dans Un Congrès Année : 2022

On the intimacy of bifunctional catalysts for the conversion of syngas to light olefins

V. Lhospital
  • Fonction : Auteur
  • PersonId : 1135539
P. Fongarland
  • Fonction : Auteur
A. Le Valant

Résumé

Context and objectives Light olefins (C2–C4) are key building-block chemicals mostly produced either by steam cracking or fluid catalytic cracking of oil resources, two highly energy-consuming processes. Among alternative processes, the syngas via methanol to olefins (SMTO) and the OX-ZEO single step processes are very promising since very high selectivity to light olefins can be reached. They combine one hydrogenating catalyst to synthesize either methanol or ketene and one acidic zeotype to convert the intermediate into light olefins. In both cases, the intermediate has to diffuse from the first catalyst to the other and their intimacy can significantly influence the catalytic performances. In this work, Cu/ZnO/Al2O3 or MnOx was used as hydrogenating catalyst and SAPO-34 as acidic zeotype The role of intimacy has been investigated by modulating the density of contact between the two functions in different bed arrangements and the distance through preparing MnO@SiO2 core shell structures or diluting the two catalysts in SiO2. Material and methods Cu/ZnO/Al2O3 was commercial catalyst while MnOx and MnOx@SiO2 were prepared from MnCO3 powder or monodispersed suspension by different routes. SAPO-34 powders with different acidities were prepared by hydrothermal method. The catalysts were characterized before and after reaction by various techniques, including ICP/XRF, BET, H2 and CO-TPR, NH3-TPD, XRD, SEM, STEM-HAADF, NMR as well as by in situ DRIFT and Raman spectroscopies. Catalytic performances were compared using a fixed-bed reactor with a feed H2/CO/N2:62/23/15 at 390-450 °C and 25 bar. Main results For both catalytic systems, methanol was shown to be a key intermediate from catalytic data and from the in situ DRIFT observation and evolutions of formates (Fig. 1a) which are formed before methoxy species. The two catalytic systems were active and selective (>50%) to C2-C4 hydrocarbons with a low Olefin/Paraffin (O/P) ratio (<0.3) when using Cu/ZnO/Al2O3 and high (up to 8) using MnOx with SAPO-34. Different parameters such as the pre-treatment temperature, the SAPO-34 acidity and the conversion were shown to strongly influence this ratio. After optimizing the mass balance for the two systems, it was shown that the conversion raised increasing the number of catalytic bed layers and hence the density of contact. It was further increased for random mechanical mixtures but only without milling. On the contrary, the disappearance of contact depositing even a thin shell of SiO2 over MnOx cores or strongly diluting MnOx into SiO2 led to a drop of conversion associated with a strong increase in CH4 selectivity. Crossing NH3-TPD and SEM images, the conversion was shown to depend on the surface interaction between Cu/ZnO/Al2O3 and SAPO-34 generating particular active sites. For MnOx+SAPO-34, a strong morphological modification under feed was evidenced by SEM (Fig1b and c) revealing intimacy was in situ generated. Attempts to strengthen this intimacy was unsuccessful. Major conclusions This work evidenced the key role of intimacy of bifunctional catalysts for the conversion of syngas to light olefins. For both Cu/ZnO/Al2O3 and MnOx catalysts associated with SAPO-34, the conversion was maximal for simple mechanical mixtures. It arises from two totally different phenomena.
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Dates et versions

hal-03681061 , version 1 (30-05-2022)

Identifiants

  • HAL Id : hal-03681061 , version 1

Citer

C. Coudercy, V. Lhospital, R. Checa, P. Fongarland, A. Le Valant, et al.. On the intimacy of bifunctional catalysts for the conversion of syngas to light olefins. FCCAT 3 2022, May 2022, Ronce-les-Bains, France. ⟨hal-03681061⟩
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