Enhanced Direct Dimethyl Ether Synthesis from CO2-Rich Syngas with Cu/ZnO/ZrO2 Catalysts Prepared by Continuous Co-Precipitation

Abstract

The manufacturing of technical catalysts generally involves a sequence of different process steps, of which co-precipitation is one of the most important. In this study, we investigate how continuous co-precipitation influences the properties of Cu/ZnO/ZrO2 (CZZ) catalysts and their application in the direct synthesis of dimethyl ether (DME) from CO2/CO/H2 feeds. We compare material characteristics investigated by means of XRF, XRD, N2 physisorption, H2-TPR, N2O-RFC, TEM and EDXS as well as the catalytic properties to those of CZZ catalysts prepared by a semi-batch co-precipitation method. Ultra-fast mixing in continuous co-precipitation results in high BET and copper surface areas as well as in improved metal dispersion. DME synthesis performed in combination with a ferrierite-type co-catalyst shows correspondingly improved productivity for CZZ catalysts prepared by the continuous co-precipitation method, using CO2-rich as well as CO-rich syngas feeds. Our continuous co-precipitation approach allows for improved material homogeneity due to faster and more homogeneous solid formation. The so-called “chemical memory” stamped during initial co-precipitation is kept through all process steps and is reflected in the final catalytic properties. Furthermore, our continuous co-precipitation approach may be easily scaled-up to industrial production rates by numbering-up. Hence, we believe that our approach represents a promising contribution to improve catalysts for direct DME synthesis.

Direct DME synthesis on CZZ/H-FER from variable CO2/CO syngas feeds

“…The CZZ catalyst was prepared by continuous co-precipitation method from metal nitrate solution and sodium bicarbonate at pH 7 using a micro jet mixer. The resulting solution was aged at 313 K for 2 h. The precipitate was ltered, dried at 383 K for 16 h and calcined at 623 K with 3 K min À1 for 4 h. The method was described in detail by Polierer et al 46 A commercial CZA catalyst was used for comparison purposes. Commercial g-Al 2 O 3 (Alfa Aesar) or a ferrierite-type zeolite H-FER 20 (FER) (Zeolyst International) were used as dehydration catalysts.…”

“…its high Cu surface area (Table 1) and the presence of ZrO 2 , which is known to promote Cu dispersion 11 and increase the activity of Cu-based catalysts in CO 2 hydrogenation to MeOH and DME. 11,35,46,52 It is interesting to note that although CZA has a relatively low copper surface area of 13 m 2 g À1 CZA/FER offers high DME productivities: with pure H 2 /CO 2 (according to CO 2 /CO x ¼ 1) at 523 K, the productivity is only 9% lower than using CZZ/FER (CZZ-S Cu : 27 m 2 g À1 ).…”

Improved Preparation of Cu/Zn‐Based Catalysts by Well‐Defined Conditions of Co‐Precipitation and Aging

“…This overlap happens because the supply of reactants requires several minutes and aging usually takes another 30 min to several hours, while the co-precipitation is completed in milliseconds to seconds [22,33]. Thus, freshly precipitated particles and particles that have already aged for up to 20 to 60 min [17,29,31], coexist with this procedure. A locally limited supply of reactant solutions and the inhomogeneous mixing conditions in the stirred tank reactor may also contribute to the spatial inhomogeneity of the co-precipitation and aging parameters.…”

Continuous synthesis of Cu/ZnO/Al2O3 nanoparticles in a co-precipitation reaction using a silicon based microfluidic reactor

“…However, for larger quantities and industrial applications a semi-batch or continuous process would be advantageous. [26][27][28][29] Catalytic performance of Cu/ZnO/(Al 2 O 3 ) is particularly influenced by the surface area of copper (SA Cu ) and the area of reactive interface with ZnO in a nanoparticulate and porous structure. 30 Metallic Cu clusters/particles are considered to be the most active sites for methanol synthesis, strongly improved by ZnO, 2,25 and Al 2 O 3 as a structural promoter 25,29 reducing NP sintering.…”