Synthesis Gas to Hydrocarbons over CuO-CoO-Cr2O3/H+-ZSM-5 Bifunctional Catalysts

CuO-CoO-Cr 2 O 3 /H + -ZSM-5 (C3Z) bifunctional catalysts were prepared for CO hydrogenation to hydrocarbons. The CO conversion and hydrocarbon distribution were measured in a fixed bed flow reactor, operating at 275 to 400 °C, 300 to 1200 h −1 gas hourly space velocity (GHSV), and 700 to 1500 psig pressure. It was found that the catalyst has relatively high activity and selectivity in producing aromatic hydrocarbons. The CO conversion, hydrocarbon selectivity, and hydrocarbon distribution as a function of temperature, pressure, GHSV, H 2 /CO ratio of the feed, and reaction time were examined. The increase of temperature and pressure favors carbon monoxide conversion and formation of higher hydrocarbons, the selectivity to hydrocarbons increased with decreasing of the H 2 /CO ratio and space velocity of the feed gas. CO conversion decreased by ∼5% after 170 h run at 350 °C and H 2 /CO ratio of 1, while the selectivity to methane increased with reaction time, C5 + fractions decrease slightly, and aromatics almost remained constant, which may be due to copper sintering under reaction conditions. The catalyst was also investigated under a syngas containing 56.5 ppm H 2 S and it was found that the catalyst lost its activity gradually with increasing H 2 S/Cu ratio. The catalysts were characterized by physisorption and temperature-programmed reduction (TPR). The surface area of the used CuO-CoO-Cr 2 O 3 is less than that of the fresh CuO-CoO-Cr 2 O 3, which confirms that catalyst sintering may occur during reaction, thus resulting in modification of the catalyst structure. XRD results demonstrated that Cu, Co, and Cr were mainly present as CuO, Co 3 O 4, and Cr 2 O 3 in the as-prepared catalysts, copper oxide was reduced to copper metal, Co 3 O 4 was reduced to CoO, while Cr 2 O 3 remained unchanged after reaction. XPS results showed Cu, Co, and Cr mainly present as Cu 2+, Co 2+ /Co 3+, and Cr 3+ in the fresh catalyst sample surface, almost 100% copper is Cu 0 in the used catalyst and cobalt mainly exists as Co 2+ after reaction, chromium is almost unchanged after reaction. The morphology and particle distribution of the C3Z samples were also characterized by using SEM and TEM. SEM and TEM images proved copper sintering and segregation from CoO-Cr 2 O 3 and H + /ZSM-5 and led the deactivation of the catalyst.