New insights into methanol synthesis catalysts from X-ray absorption spectroscopy

Abstract

X-ray absorption spectroscopic studies from several different groups provide a consistent structural picture of methanol synthesis catalysts. Copper metal is the principal Cu species detected in all in-situ XAS studies. A small amount of Cu(II) persisted in many samples reduced below 600 K, but it appears to be catalytically irrelevant. Cu(I) was not detected in any of the in-situ XAS studies. The Zn structure did not change in response to chemical treatments in any of the ZnO-containing methanol synthesis catalysts.We conclude that the slow approach to steady-state rate of methanol synthesis from CO/H 2 mixtures cannot result from changes in the Cu metal component of Cu/SiO 2 catalysts. By eliminating this possibility, we provide indirect evidence for the proposal that initial induction periods reflect slow changes in the surface of the SiO 2 or ZnO component in the catalysts. A bifunctional mechanism involving the formation of formate from CO on support hydroxyl groups would increase methanol synthesis rates as OH groups are formed by hydrolysis of Si-O bonds using the H 2 O formed in slow methanation side reactions. The bifunctional mechanism is not required for the synthesis of methanol from CO 2 -containing mixtures, because formate can form on Cu directly from CO 2 and H 2 .

Rapid Kinetic Measurements in Ammonia and Methanol Syntheses

“…37 On the other hand, Lee et al 34 reported that steady-state rates were reached in catalytic experiments with a Cu/ZnO/ Al 2 O 3 catalyst after 5 and 20 h on stream for CO 2 /H 2 and CO/H 2 , respectively. A similar transient behavior has also been observed by Meitzner and Iglesia 33,35 for Cu/SiO 2 . The catalytic activity decreased gradually when they were feeding CO 2 to a CO/H 2 /N 2 mixture.…”

“…Similar behavior observed for binary and ternary Cu systems has been reported in the literature. [33][34][35] The highpressure measurements were conducted over a lowtemperature range from 433 to 513 K. The resulting production rates calculated from the outlet CH 3 OH concentration assuming differential conditions are displayed versus the inverse temperature in a so-called Arrhenius plot (Figure 4). It can be seen that the differences in the production rates of the three catalysts are small.…”

Methane dehydroaromatization over Mo/HZSM-5 catalysts in the absence of oxygen: effects of silanation in HZSM-5 zeolite

“…Iglesia and coworkers suggested that most of the MoC x species should be resided in the channels [24][25][26][27][28][29]. This opinion has been further demonstrated with 1 H MAS NMR measurements on the Mo/HZSM-5 catalysts prepared by impregnation by Bao and coworkers [30].…”

Growth of Copper on Single Crystalline ZnO: Surface Study of a Model Catalyst

“…(vi) Cu + ions are active sites for CO adsorption and hydrogenation reactions [9,10,20]. The Cu + may be stabilized at the Cu/ZnO interface or are found as dissolved Cu in the ZnO particles [2,17,[21][22][23][24]. As pointed out by Nakamura et al more than one synergetic effect between Cu and ZnO may explain the high efficiency of this catalyst for methanol synthesis.…”