Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1998-01-22
2000-02-01
Griffin, Steven P.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502250, 502315, 502316, 502336, 502338, 585270, 585267, 585328, B01J 2108, B01J 2300, B01J 2370, C07C 510
Patent
active
060202858
DESCRIPTION:
BRIEF SUMMARY
This invention relates to catalysts and in particular to catalysts, or precursors thereto, containing an inert support material and at least one oxide of a metal of Group VIII of the Periodic Table and selected from nickel and cobalt.
In our EP 0 397 342 we describe catalysts in the form of shaped particles, e.g. extrudates, containing a calcium aluminate cement, an oxide of cobalt and/or nickel, and optionally a finely divided diluent material, the shaped particles having specified porosity and specified pore size distribution characteristics. These catalysts were of particular utility for the decomposition of hypochlorite ions in an aqueous medium.
In that specification we indicated that increasing the porosity of the particles was desirable as it allows the reactants to have ready access to the active material within the particles. However this had the disadvantage that the strength of the particles was decreased.
We have now found that by employing a calcium aluminate cement having a high alumina content, the porosity can be increased without undue loss of strength and as a result the activity of the catalyst can be increased. Surprisingly, despite the higher porosity, the bulk density of the particles can be increased so that a greater mass of particles, and hence active material, can be accommodated in a catalyst bed of given volume. [The bulk density is determined by filling a vessel of known volume with the catalyst particles, with tapping of the vessel to ensure that the particles settle, and then determining the weight of particles in the vessel.]
Calcium aluminate cements are hydraulic cements containing one or more calcium aluminate compounds of the formula nCaO.mAl.sub.2 O.sub.3 where n and m are integers. Calcium aluminate compounds mentioned in the aforesaid specification include calcium mono-aluminate CaO.Al..sub.2 O.sub.3, tri-calcium aluminate 3CaO.Al.sub.2 O.sub.3, penta-calcium tri-aluminate 5CaO.3Al.sub.2 O.sub.3, tri-calcium penta-aluminate 3CaO.5Al.sub.2 O.sub.3, and dodeca-calcium hepta-aluminate 12CaO.7Al.sub.2 O.sub.3. The calcium aluminate cement used in the examples of that specification had an aluminium to calcium atomic ratio of about 1.4. By the term high alumina cement, we mean a calcium aluminate cement having an aluminium to calcium atomic ratio above 2.5. Such cements are known and may contain one or more of the above calcium aluminate compounds, and or compounds such as calcium di-aluminate CaO.2Al.sub.2 O.sub.3, in some cases with additional alumina.
Accordingly the present invention provides shaped particles suitable for use as a catalyst, or precursor thereto, comprising a calcium aluminate cement having an aluminium to calcium atomic ratio above 2.5, and preferably above 4.0, and at least one oxide of a Group VIII metal M selected from nickel and cobalt, said particles containing 10 to 70% by weight of said Group VIII metal oxide (expressed as the divalent oxide, MO) and having a porosity in the range 30 to 60%, particularly 40 to 55%, in which at least 10% of the pore volume is in the form of pores of size in the range 15 to 35 nm and less than 65% of the pore volume is in the form of pores of diameter greater than 35 nm.
As described in the aforesaid EP 0 397 342, for some catalytic applications the Group VIII metal oxide is the catalytically active species while for other catalytic applications the Group VIII metal oxide is a catalyst precursor and the catalytically active species is the product of reducing the Group VIII metal oxide to the Group VIII metal or is the product of oxidising the Group VIII metal oxide in the precursor to a higher oxidation state. For example catalysts obtained by reduction of a precursor containing nickel and/or cobalt oxide are of use as hydrogenation catalysts, e.g. methanation catalysts for the hydrogenation of carbon oxides to methane or catalysts for the hydrogenation of aromatic compounds such as benzene to cyclohexane. Another use of supported nickel and/or cobalt oxides is as catalysts for the decomposition of oxidising agents
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Griffin Steven P.
Imperial Chemical Industries plc
Nguyen Cam N.
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