Effect of Water Layer in a Microreactor on the Low-Temperature Synthesis of High-Activity Cu/ZnO Catalysts

Abstract

The effect of a water layer on the precipitation process in a three-channel microreactor at low temperatures was investigated. Fourier-transform infrared spectroscopy, Xray powder diffraction, thermal gravimetric analysis, X-ray photoelectron spectroscopy, temperature-programmed reduction, and Brunauer−Emmett−Teller analysis were employed for studying the structural evolution of the intermediate products during the preparation of both zincian georgeitederived and zincian malachite-derived catalysts, and catalytic activities were measured for methanol synthesis from syngas. It is manifested that the effect of uniform precipitates acts consecutively on the subsequent aging process, Zn incorporation in precursors, thermal decomposition, reduction, and catalytic performance of the catalysts. Numerical simulation revealed the change of species properties, and reaction rates at varying temperatures can lead to different regulations of the water layer, denoting that disparate ratios of the water layer were required for obtaining uniform precipitates under different conditions, which further suggests the key role of uniformity of the precipitates in preparing high-activity Cu/ZnO catalysts.

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.…”

“…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.…”

“…In our early studies, the effects of flow and mixing inside micro‐reactors on the structure of precipitate and its evolution had been proved, which finally impacts the structure and performance of catalyst 10 . Then, the diffusion–reaction under laminar flow was investigated in a specially designed three‐channel micro‐reactor, and the numerical simulation showed the important role of diffusion on the Cu‐Zn distribution in co‐precipitate 12 . Nevertheless, the flow in micro‐reactor is more complicated and the turbulence can be formed in some sections where the flow channel changes drastically, for example, in the immediate downstream of the T‐ junction, which has the most important effect on the co‐precipitation.…”