The effect of mixing on Co‐precipitation and evolution of microstructure of Cu‐ZnO catalyst

Abstract

The influence of feeding point in conventional stirred tank reactor and flow characteristics in micro‐reactor on the microstructure of Cu‐ZnO catalyst was studied. Cu‐Zn distribution in co‐precipitate was characterized by EDS and Zn fraction in zincian malachite was estimated from the 20 true1¯ peak shift in XRD pattern. The theory analysis and experimental results, combining with measurement of segregation index, show that the contact pattern and mixing of reactants in precipitation process determine the uniformity of Cu‐Zn distribution in initial co‐precipitates at the micro‐scale. The uniform Cu‐Zn distribution is favorable for the formation of zincian malachite with higher Zn fraction, whereas the uneven distribution could lead to either zincian malachite with lower Zn fraction or aurichalcite‐like nonmalachite. These differences in the precursor structure act on subsequent calcination and reduction, as well as their products. Along this path, mixing affects the evolution of the catalyst microstructure by means of Cu‐Zn distribution. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2647–2654, 2018

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

“…For the preparation of Cu-based catalysts, different synthesis methods have been established, such as conventional batch-wise co-precipitation [26][27][28], impregnation [29], deposition precipitation [30], or flame spray pyrolysis [18,31]. However, in case of the commonly used co-precipitation, alternative manufacturing approaches have been developed, based on the fundamental knowledge obtained for the key steps of nucleation, crystal growth and ripening, that have the potential for a better control of the material properties, thus paving the way to more efficient catalysts [32][33][34][35][36][37][38][39]. For Cu-based catalysts it is known that the mixing during precipitation strongly influences the initial formation of solids with regard to solid phase distribution and morphology [19,32,34,36,[40][41][42].…”

“…However, in case of the commonly used co-precipitation, alternative manufacturing approaches have been developed, based on the fundamental knowledge obtained for the key steps of nucleation, crystal growth and ripening, that have the potential for a better control of the material properties, thus paving the way to more efficient catalysts [32][33][34][35][36][37][38][39]. For Cu-based catalysts it is known that the mixing during precipitation strongly influences the initial formation of solids with regard to solid phase distribution and morphology [19,32,34,36,[40][41][42]. In conventional semi-batch operation mode, typically performed in stirred tank type reactors, the spatial and temporally inhomogeneous precipitation conditions such as temperature or reactant concentration can then result in inhomogeneous particle formation [43][44][45].…”

Effect of turbulence in micro‐reactors on ultrafast competitive reactions in Cu‐Zn co‐precipitation

“…The pH undergoes a slow increase in early stage, an abrupt fall to a significant turning point, a rapid bounce, and another slowly increasing stage in the end. As reported in the literature, the radical change in pH during the aging process is related to the transformation from amorphous precipitates to crystalline precursors, 13,15 so we define the time at which the pH comes to the minimum as the characteristic aging time 10 . As shown in Figure 2, with the increase of flow rate, the characteristic aging time moves forward first and then moves backward.…”

“…To test this result, EDS line scanning was carried out to characterize the uniformity in precipitate 10,12 . The results of five samples above were shown in Figure 3, where (A)–(E) represent samples prepared at volume flow rates of 10, 20, 30, 40, and 50 ml/min, respectively.…”

“…The most common synthetic method is the co‐precipitation, 8,9 where co‐precipitates are formed through the rapid precipitation reaction of Cu 2+ and Zn 2+ ions. The latest studies 10‐12 have revealed that the co‐precipitation is strongly affected by the flow and mixing in reactor, which acts on the uniformity of Cu‐Zn distribution in co‐precipitates, and then has a vital effect on the subsequent structural evolution and the final catalytic performance. Due to the dependence of mixing on the reactor structure, parameters like configuration of stirrer, stirring speed, baffle size, and location of feeding port can impact the progress of co‐precipitation reaction, 13,14 which then changes the structures of precipitates and subsequent products, and finally affects the catalytic activity.…”