Coprecipitated nickel–alumina catalysts for methanation at high temperature. Part 1.—Chemical composition and structure of the precipitates

Abstract

A series of materials containing nickel and aluminium ions has been prepared by coprecipitation with alkaline solutions, under various conditions, from solutions of the nitrates. The composition and structure of the precipitates has been examined using a number of techniques including chemical analysis, X-ray diffraction, thermogravimetry and infrared spectroscopy. The precipitates have structures typical of minerals of the hydrotalcite group and particularly of the nickel-aluminium compound, takovite. They consist of brucite-like layers of composition [Ni,Al,-,(OH),](1-2)+ and interlayers containing CO:-, NO, or OH-ions, or combinations of these, depending on the preparation conditions, together with molecular water; the anions balance the excess charge of the brucite layers. It is concluded that the aluminium ions are randomly substituted for nickel ions in the brucite layers and that the structure of these layers is independent of the anions in the interlayer. For freshly precipitated samples, 0.5 < x 5 0.85, but for hydrothermally aged materials, 0.66 6 x 6 0.75; outside these ranges, boehmite or Ni(OH), form as separate phases. The results are compared with those for precipitates prepared from ammoniacal solutions and it is concluded that the two types of material are indistinguishable.

Effect of the Mg:Al Ratio on Borate (or Silicate)/Nitrate Exchange in Hydrotalcite

“…These results are similar to others previously reported for nitrate and carbonate-containing hydrotalcites (25,26). When the Mg : Al ratio decreases, the net positive charge of the layers increases and a larger concentration of interlayer anions is required.…”

“…It should be noted that for sample 4N a shoulder is also recorded around 3000 cm\. A broad shoulder in this position has been previously reported (25,32) and it has been ascribed to the stretching mode of OH groups hydrogen-bonded to interlayer carbonate anions. It is possible that similar hydrogen bonding exists in this sample where (as carbonate) the nitrate anions are in a #at position.…”

Natural gas reforming and CO2 mitigation

“…In collaboration with the group of L.L. van Reijen in Delft (The Netherlands) [5][6][7], we examined factors determining the behaviour of the co-precipitated catalysts, showing that the nature of the precipitates formed (hydrotalcites, with characteristic and well-defined layer structures) determined the subsequent behaviours of the catalysts. We then went on to develop a novel catalyst that combined the advantages of the high activities of the CRG catalysts with the mechanical stabilities imparted by a-alumina [8,9].…”

Ni–Al layered double hydroxides as catalyst precursors for CO2 removal by methanation

“…In a series of articles [57][58][59][60][61] Kruissink et al have claimed that a thermal treatment of co-precipitated Ni-Al precursors of Ni 2? /Al 3?…”