Phase-Pure Cu,Zn,Al Hydrotalcite-like Materials as Precursors for Copper rich Cu/ZnO/Al 2 O 3 Catalysts Malte Behrens, et al.,Chem. Mater., 22, 2, 2010, 386 Zincian malachite or rosasite (Cu,Zn) 2 (CO 3 )(OH), aurichalcite (Cu,Zn) 5 (CO 3 ) 2( OH) 6, and hydrotalcite-like (htl) materials of the general composition ((Cu,Zn) (1-x) Al (x) (OH) 2 (CO 3 ) x/2. 3 m H 2 O are the typical hydroxy carbonate precursor phases for Cu-ZnO/Al 2 O 3 catalyst An intimate mixture of the oxides can be obtained by calcination. Afterward,the CuO component is reduced yielding highly dispersed and catalytically active Cu. Mostly empirical optimization has led to a preparation route based on coprecipitation of mixed solutions to obtain catalyst precursors usually comprised of a phase mixture of the different hydroxy carbonates These mixtures are not easy to characterize comprehensively due to the varying Cu:Zn ratios of the single phases and their typically low crystallinity. However, it can be expected that all components of the precursor lead to different domains in the Cu/ZnO/Al 2 O 3 catalysts with different types of material and individual catalytic properties. Together, these domains make up the highly active industrial system causing an in homogenous microstructure The general structure of htl compounds, being built of brucite-like M 2+ (1-x) M 3+ (x) (OH) 2 (CO 3 ) x/2 layers and charge compensating interlayer anions In CuZnAl htl compounds all three metal species share the octahedrally coordinated sites in the layers and are, thus, evenly distributed on an atomic level within a single Phase. Hence, formation of catalysts of a homogeneous microstructure exhibiting high dispersion of the metal species and enhanced metal-oxide interaction after reduction can be expected. In this paper the synthesis and characterization of a series of five Cu/ZnO/Al 2 O 3 catalysts (Cu:Zn = 70:30) derived from phase pure CuZnAl htl precursors with Al contents between % will be discussed. The effects of the precursor composition on the microstructure and the catalytic performance of the final catalysts will be investigated Hydrotalcite-like compounds exhibit positively charged brucitic (MII,MIII)(OH)2 layers, which are built from edge-sharing octahedra, and charge compensating interlayer anions. Here, a couple of adjacent layers and two possible positions for the carbonate anions in the interlayer space are shown. Interlayer water molecules are not shown for clarity Catalyst Preparation NaOH and Na 2 CO 3 were added ( pH = 8) Precipitate Precipitate aged at 25C for 1h Obtained ppt was washed and dried at 60C over night Cu-Zn-Al HTL Calcined in air for with different temperature ((Cu,Zn) (1-x) Al (x) (OH) 2 (CO 3 ) x/2.3 m H 2 O x= 0.3, 0.325, 0.35, 0.375, and 0.4 Cu:Zn = 70 : 30 CuO-ZnO-Al 2 O 3 Metal Compositions of the htl precursors in This Study, Calcination Temperatures, and Specific Surface Areas of the Calcination Products Nominal concentration normalized to the total metal content, values measured by ICP are given in parentheses. b Hydrodynamic diameter ((5 nm) c BET surface area determined by N 2 physisorption XRD patterns of the htl precursor materials Variations of XRD peak positions of the 006 reflections (full symbols) and the 11 bands (open symbols) and half-widths of the 003 peaks (+) as a function of Al content. TGA-MS curves for the thermal decomposition of 30-htl (full lines) and 40-htl (dotted lines) in air (a) and XRD patterns of the sample after calcination at 330 C (b). The red arrows mark the different calcination temperatures for the sample 30-htl XRD patterns of the precursor 30-htl after calcination at different temperatures and after heating to 700 C during TGA. The final product can be identified as a mixture of CuO (blue) and ZnAl 2 O 4 (red). SEM micrographs of the samples (a) and (b) IR spectra of the samples 30-htl, , and TEMimages of the sample with typical amorphous areas (a, upper right part, and b) and less common granular areas (a, lower left part,and, c); (d) Zn-depleted amorphous platelets in The lattice distance in (c) of 2.53A corresponds to the -111 spacing of CuO Cross section TEM of an agglomerate of platelets in sample and EDX mapping showing a homogeneous distribution of the metals in the platelets and agglomerates TEMmicrograph and corresponding copper particle size distributions of the areas originating fromthe amorphous (a, upper left part, red, also other areas were used for determination of the size distribution shown) and granular (a, lower right part, blue) areas in the sample after reduction. Images of the microstructure of the previously amorphous (red) areas at higher magnification (b, c). TPR profiles of the htl samples calcined at 330 C A, initial state of htl precursor with perfect distribution of all species, the element symbols represent the metal ions with their oxygen surrounding; B, loss of interlayer water and hydroxyl groups from the layers, carbonate remains in the material, start of Al segregation to fulfill the Zn:Al ratio of 1:2 for spinel formation (two Al meet at a Zn site, Cu and Zn remain static); C, resulting microstructure with Al depleted (Cu rich)and dense Al-rich areas, emission of CO 2 from the former areas due to crystallization of CuO D, decomposition of residual carbonate and complete segregation into crystalline CuO and ZnAl 2 O 4 CuZnAl hydrotalcite-like compounds are suitable precursors for Cu/ZnAl2O4 catalysts of homogeneous microstructure, if their Zn:Al ratio is close to 1:2 If the Zn:Al ratio of the htl precursor in the phase mixture significantly deviates from 1:2, formation of more than one Cu species in the final catalyst can be expected The preformed spinel and CuO phase will not separate or crystallize at low calcination temperatures and an amorphous carbonate-modified form of a mixed oxide is formed The Cu particles formed from this amorphous material are extraordinary small, but to a large extent embedded into the amorphous ZnAl 2 O 4 matrix Upon reduction, very small (ca. 7 nm) Cu particles are formed from the amorphous material. The maximal rate of reduction is observed at relatively high temperatures well above 200 C. The homogeneous distribution of active and refractory components in the catalyst and the extraordinary small Cu particle size renders the htl precursor system promising for preparation of Cu based catalysts