Single-step synthesis of dimethyl ether from syngas on Al2O3-modified CuO–ZnO–Al2O3/ferrierite catalysts: Effects of Al2O3 content

The role of the acidity of alumina prepared by aluminum-carbon black composite for CO hydrogenation to dimethyl ether on hybrid Cu–ZnO–Al2O3/alumina

“…The direct relationships of the total amount of acid sites and the surface area of metallic copper to the catalytic activity for a direct synthesis of DME from syngas have been well reported in our previous works [7,12,14,23]. In general, a larger surface area of metallic copper and a proper amount of acid sites are known to be responsible for a higher CO conversion, and the stability of hybrid catalysts has been generally known to be related with a stability of metallic copper species on the acid sites [3,7,18,19,23,24].…”

“…c-Al 2 O 3 was easily synthesized by using the carbon black-alumina composites, where carbon black acts as an adjusting material of the pore size and surface area of c-Al 2 O 3 . Even though the contributions of the surface area of metallic copper and acidity of solid-acid components were well reported in our previous works [7,11,12,14], the acidic and structural contribution of the easily tunable c-Al 2 O 3 structures to the catalytic activity and the dispersion of copper-containing particles were not sufficiently reported as far as we know. Therefore, the effects of the acidity and the structure of c-Al 2 O 3 derived from carbon black-alumina composites on the dispersion of Cu-ZnO-Al 2 O 3 and the catalytic activity were explained by measuring the acidity and the surface area of the hybrid catalysts with the enhanced stability of the active copper-containing particles after reaction.…”

“…The characteristic vibration peaks for the CuO and c-Al 2 O 3 on the hybrid CZA/Al 2 O 3 was observed at *830 and 1730 cm -1 and at *1050 and 1260 cm -1 , respectively [9,14,16]. The electronic images and crystallite sizes of copper oxides with the variations of surface morphologies before and after reaction were also characterized by using the transmission electron microscopy (TEM; TECNAI G2) to further verify the results of XRD and N 2 O titration on the selected fresh and used CZA/Al 2 O 3 (0) and CZA/ Al 2 O 3 (10).…”

“…The aqueous solution of ammonium carbonate as a precipitant and the aluminum precursor solution were separately dropped in the slurry of carbon black at 70°C by using a syringe pump to precisely adjust the dropping rates, and aged for 1 h at the same temperature. The solution color was altered from blue to green-blue at the neutral point of pH = 7 [14]. The precipitate was filtered and washed with hot deionized water for removing the remained ammonium ions and subsequently dried for a day at 80°C.…”

“…Before the reaction, the asprepared hybrid catalyst was previously reduced by using 5 % H 2 balance N 2 gas at 300°C at an ambient pressure for 7 h. The DME synthesis reaction was carried out under T = 250°C, P = 5.0 MPa, and space velocity = 2000 L/kg cat /h with the catalyst loading of 0.4 g using the syngas having a molar composition of CO/H 2 / N 2 = 31.5/63/5.5 with internal standard gas of N 2 , which are typical conditions for verifying the catalytic activity from our previous works [7,11,12,14]. The asprepared hybrid catalyst was sieved and only the size in the range of 60-100 lm was selected for the activity test, which has been recommended as a proper particle size with negligible external mass-transport limitations [15], and the kinetic control of the activity was also verified experimentally by observing similar catalytic activities with a different catalyst loading of 0.1 g at the same space velocity.…”