NiO/MgO catalyst

The conversions and selectivities remained unchanged during the entire reaction time employed (120 h), indicating that the reduced NiO/MgO catalyst had a high stability (Fig. 14). 

From the above results, one can conclude that different NiO/MgO solid-solution catalysts can have very different catalytic performances. For example, Fujimoto et aV s Nio.03Mgo.97O solid-solution catalyst exhibited relatively low activities. To reach about 82% conversion of CH4 in the presence of this Nio.03Mgo.97O catalyst, the space velocity had to be reduced to 18,670 mL (g catalyst)-1 h-1 at 1123 K (Fig. 15) (238). In contrast, Ruckenstein and Hu s NiO/MgO catalysts have very high activities (>91% conversion of CH4 and >95% selectivities of CO and H2 at the space velocity of 60,000 mL (g catalyst)-1 h-1 at 1063 K) (Fig. 14) (239). Hu and Ruckenstein (239,257,259) noted that the properties of the MgO, such as its surface area, pore size distribution, and crystal structure, have important effects on the NiO/MgO solid-solution catalysts. They found that the MgO supplied by Aldrich, which has... 

In summary, the basicity and the strong NiO-MgO interactions in binary NiO/MgO solid solution catalysts, which inhibit carbon deposition and catalyst sintering, result in an excellent catalytic performance for C02 reforming. The characteristics of MgO play an important role in the performance of a highly efficient NiO/MgO solid-solution catalyst. Moreover, the NiO/MgO catalyst performance is sensitive to the NiO content a too-small amount of NiO in the solid solution leads to a low activity, and a too-high amount of NiO to a low stability. CoO/MgO solid solutions have catalytic performances similar to those of NiO/MgO solid solutions, but require higher reaction temperatures. So far, no experimental information is available regarding the use of a FeO/MgO solid solution for CH4 conversion to synthesis gas. 

Yang, Z., Ding, W., Zhang, Y, et al. (2010). Catalytic Partial Oxidation of Coke Oven Gas to Syngas in an Oxygen Permeation Membrane Reactor Combined with NiO/MgO Catalyst, Int. 

MgO is a basic metal oxide and has the same crystal structure as NiO. As a result, the combination of MgO and NiO results in a solid-solution catalyst with a basic surface (171,172), and both characteristics are helpful in inhibiting carbon deposition (171,172,239). The basic surface increases C02 adsorption, which reduces or inhibits carbon-deposition (Section ALB). The NiO-MgO solid solution can control the nickel particle sizes in the catalyst. This control occurs because in the solid solution NiO has strong interactions with MgO and, as indicated by TPR data (26), the former oxide can no longer be easily reduced. Consequently, only a small amount of NiO is expected to be reduced, and thus small nickel particles are formed on the surface of the solid solution, smaller than the size necessary for coke formation. Indeed, the nickel particles on a reduced 16.7 wt% NiO/MgO solid-solution catalyst were too small to be observed by TEM (171). Furthermore, two additional important qualities stimulated the selection of MgO as a support its high thermal stability and low cost (250,251). 

In 1989, Gadalla and Sommer (252) reported that a solid-solution NiO/MgO (1 1.35) catalyst prepared by precipitation can inhibit the carbon deposition in the CO2 reforming of methane however, they obtained a low CO2 conversion (66%), a low H2 selectivity (79%), and a low CO selectivity (77%), even at the very low WHSV of 3714 cm3 (g catalyst)-1 h-1 with a CH4/CO2 (1/1, molar) feed gas and the high temperature of 1200 K. Their relatively high CH4 conversion was partly a consequence of homogeneous gas-phase reactions that occurred under their conditions. Indeed, the authors found extensive carbon deposits plugging the reactor upstream and downstream of the reaction zone. 

Recently, Ruckenstein and Wang (264-266) also successfully developed excellent CoO/MgO solid-solution catalysts for C02 reforming of methane. They reported that Co/MgO exhibited a good catalytic performance with a CO yield of 93% and a H2 yield of 90% at the high space velocity of 60,000 mL (g catalysts)-1 h-1 and 1163 K, which remained unchanged during 50 h of investigation (264). In contrast, Co/CaO, Co/SrO, and Co/BaO each provided low CO yields, and Co/CaO also had a low stability. The results indicate that the CoO/MgO catalysts are characterized by performances similar to those of NiO/MgO. 

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