High-performance Cu/ZnO catalysts prepared using a three-channel microreactor

Comparative study on the effect of different copper loading on catalytic behaviors and activity of Cu/ZnO/Al2O3 catalysts toward CO and CO2 hydrogenation

“…The XRD patterns of CZA-H and CZA-L catalysts are shown in Figure 1. The XRD patterns for both catalysts are quite similar showing no peaks of malachite [(Cu, Zn) 2 (OH) 2 CO 3 ], which supposed to locate at 24.1 and 31.2 (Behrens et al, 2011;Jiang et al, 2019) and aurichalcite [(Cu, Zn) 5 (OH) 2 CO 3 ] with the expected characteristic peaks at 27.0 and 31.8 (Yang et al, 2018;Jiang et al, 2019), which were referred to the residue originating from the catalyst precursor without complete decomposition during the calcination process. On the other word, all residues were removed after calcination.…”

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

“…As shown in Figure 2, with the increase of flow rate, the characteristic aging time moves forward first and then moves backward. It was found in our previous research, the characteristic aging time is closely corresponding to the homogeneousness in co‐precipitates, and the better uniformity of Cu‐Zn distribution in precipitates brings about shorter characteristic aging time 10‐12 . Usually, the better mixing makes the reaction more homogeneous in the reactor, resulting in a better uniformity of Cu‐Zn distribution in precipitates.…”

“…However, subtle differences can be detected at local areas, and the ratios of Cu, Zn are fluctuating around average. To quantify the uniformity of Cu‐Zn distribution, the data in the figure were further processed by means of the Pearson coefficient, which gets closer to one for more uniform Cu − Zn distribution 11 . The Pearson coefficients for samples from (A) to (E) in Figure 3 are 0.919, 0.944, 0.963, 0.906, and 0.888, respectively, suggesting the uniformity of Cu‐Zn distribution gets better first and worse then, which is consistent with the conclusion gotten from the characteristic aging time.…”

“…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.…”

“…It has been found 16‐19 that during the aging process, the pH first undergoes a slow increase, then a rapid fall and rise followed by another slowly increasing stage in the end, and the radical change in pH is related to the transformation from amorphous precipitates to crystalline precursors. The Cu‐Zn distribution in co‐precipitates from EDS analysis showed that the turning point in pH is dependent on the homogeneousness in co‐precipitates and more uniform co‐precipitates correspond to earlier turning point 11 . It is more crucial that the different Cu‐Zn distributions in precipitates will impact the Zn content in precursors of zincian malachite, which results in the discrepancy both in Cu‐Zn interaction of mixed oxides formed after calcination and in the performance of final catalysts obtained from further reduction.…”