Promotion effect of iron addition on the structure and CO2 hydrogenation performance of Attapulgite/Ce0.75Zr0.25O2 nanocomposite supported Cu-ZnO based catalyst

A series of CZF(x)K/ATP-CZO catalysts (x= 0, 0.3, 0.5, 1.0, 1.5 and 2.0) are applied to clarify the effects of the iron addition on the catalytic performance of CO2 hydrogenation to CH3OH. The physicochemical properties and catalytic mechanism were investigated by N-2 adsorption/desorption, XRD, TEM, N2O chemisorption, XPS, H-2-TPR, CO2-TPD and in-situ DRIFT techniques. The best catalytic performance is achieved over CZF(0.5)K/ATP-CZO catalyst, exhibiting X-CO2 = 17.5%, STYCH3OH = 0.108 g/gcat.h and STYCO = 0.146 g/gcat.h (T = 320 degrees C, P = 6 MPa). The formation of dispersed surface metallic Cu species and larger number of surface adsorbed and lattcie oxygen species and ZnO-CZO interfaces are detected over CZF(0.5)K/ATP-CZO due to stronger interaction between dispersed metallic Cu particles on ZnO-Fe nano-cluster and ATP-CZO composite, resulting in the superior activation ability for H-2 and CO2 respectively. Additionally, the evidence is provided by in-situ DRIFTS under the activity test temperature (320 degrees C) that HCOO* and CO* species are preferable for accumulating over CZK/ATP-CZO catalyst without Fe addition while medium Fe-modified CZF(x)K/ATP-CZO catalysts (CZF(0.3)K/ATP-CZO, CZF(0.5)K/ATP-CZO) catalysts are benefitial to promote the transformation of HCOO* species to CH3OH. These excessive Fe-modified CZFxK/ATP-CZO catalysts (CZF(1.0)K/ATP-CZO, CZF(2.0)K/ATP-CZO) are more easily to produce CH4 via formate pathway (CO2* -> HCOO* -> HCO* -> CH* -> CH4*). The abundant population and high transformation activity of formate intermediate species over CZF(0.5)K/ATP-CZO give a strong positive effect on the CO2 hydrogenation to methanol performance.