Performance Improvement of Nanocatalysts by Promoter-Induced Defects in the Support Material: Methanol Synthesis over Cu/ZnO:Al

Abstract

Addition of small amounts of promoters to solid catalysts can cause pronounced improvement in the catalytic properties. For the complex catalysts employed in industrial processes, the fate and mode of operation of promoters is often not well understood, which hinders a more rational optimization of these important materials. Herein we show for the example of the industrial Cu/ZnO/Al2O3 catalyst for methanol synthesis how structure-performance relationships can deliver such insights and shed light on the role of the Al promoter in this system. We were able to discriminate a structural effect and an electronic promoting effect, identify the relevant Al species as a dopant in ZnO, and determine the optimal Al content of improved Cu/ZnO:Al catalysts. By analogy to Ga- and Cr-promoted samples, we conclude that there is a general effect of promoter-induced defects in ZnO on the metal-support interactions and propose the relevance of this promotion mechanism for other metal/oxide catalysts also.

Coprecipitation: An excellent tool for the synthesis of supported metal catalysts – From the understanding of the well known recipes to new materials

“…It is schematically shown in Figure 1 and it comprises co-precipitation [24] and ageing [25][26] of a mixed Cu,Zn,(Al) hydroxy-carbonate precursor material [27], thermal decomposition yielding an intimate mixture of the oxides and finally activation of the catalyst by reduction of the Cu component [28]. The major trick of this synthesis is that under beneficial conditions the co-precipitated precursor material can be synthesized as a single homogeneous and well-defined precursor phase, zincian malachite (Cu,Zn) 2 (OH) 2 CO 3 , with a mixed cationic sub-lattice that contains all components of the catalyst and can even accommodate small amounts of the Al 3+ promoter [29] in a solid solution. This perfect distribution leads to an effective dilution of the active Cu component and is the basis for a successful nano-structuring of the precursor upon decomposition into CuO/ZnO and for the high Cu/ZnO-interdispersion in the final reduced catalyst.…”

Influence of Impregnation and Coprecipitation Method in Preparation of Cu/ZnO Catalyst for Methanol Synthesis

“…The effect of the presence of Al on the catalyst activity has been studied by Bahrens, et al [4]. The best concentration of Al was about 3-4% of the mass fraction of Al to (Cu+Zn+Al).…”

Methanol steam reforming behavior of copper impregnated over CeO 2 –ZrO 2 derived from a surfactant assisted coprecipitation route

“…The commercial MSR catalyst Cu/ZnO/Al2O3 contains a high loading of Cu and ZnO and a relatively lower amount of Al2O3 [12]. The ZnO improves the dispersion and redox properties of copper and is responsible for strong metal support interaction [13,14].…”

“…The ZnO improves the dispersion and redox properties of copper and is responsible for strong metal support interaction [13,14]. Alumina is shown to have structural and electronic promotional effect on ZnO by inducing lattice defect and increasing its reducibility [12]. In general, the addition of Al2O3 leads to the improvement of surface area of the support [11,13].…”