CO_2 Reforming and Simultaneous CO_2 and Steam Reforming of Methane to Syngas over Co_xNi_(1-x)O Supported on Macroporous Silica-Alumina Precoated with MgO

摘要

Reaction of CO_2 with methane in the absence and presence of steam over Co_xNiO_(1-x) (x = 0.0-0.5) supported on commercial macroporous silica-alumina catalyst carrier (SA-5205, obtained form M/S Norton Co. U.S.A.) precoated with MgO at different temperatures (700°-900°C) and contact times (0.03-0.3 s at STP) has been investigate.d With the increasing Co/Ni ratio of the catalyst, its surface area is decreased and its degree of reduction by H_2 at 900°C (for 1h) is increased. TPR (from 100°to 900°C) of the catalysts indicated that the NiO-CoO-MgO in the catalyst exists as a solid solution. The influence of Co/Ni ratio of the catalyst and feed ratios [CO_2/CH_4 = 0.8-1.2 in the CO_2 reforming and (CO_2+H_2O)/CH_4 = 1.2 and CO_2/H_2O = 0.4-2.0 in the simultaneous CO_2 and steam reforming] on the conversion and selectivity or H_2/CO product ratio has also been thoroughly investigated. When the Co/Ni ratio is increased, in the CO_2 reforming, the carbon deposition on the catalyst is reduced drastically and the conversion of methane and CO_2, H_2 selectivity and H_2/CO ratio is passed through a maximum. The conversion in the simultaneous CO_2 and steam reforming is also passed through a maximum, at the Co/Ni ratio of about 0.17. The supported catalyst with Co/Ni ratio of 0.17 shows high methane conversion activity (methane conversion > 95%) and 100% selectivity for both CO and H_2 with H_2/CO ratio varying from 1.2-2.2 in the simultaneous CO_2 and steam reforming processes at a high space velocity. The H_2/CO ratio can be controlled by manipulating the H_2O/CO_2 ratio in the feed; it is increased with increasing the H_2O/CO_2 ratio and vice versa.