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1、coldysisT&y,II(I99I)173-301173ElsevierSciencePublishersB.V.,AmsterdamHYDROTALCITE-TYPEANlONlCCLAYS:PREPARATION,PROPERTIESANDAPPLICATIONS.F.Cavani,F.Trifirb,A.VaccariDipartimentodiChimicaIndustrialeedeiMaterialiWalede1Risorgimento4,40136BOLOGNA(Italy).1.HISTORICA
2、LBACKGROUNDResearchintohydrotalcite-likecompoundsandcatalysisfollowedseparateparallelpathsuptotheyear1970,whenthefirstpatentappearedthatreferredspecificallytoahydrotalcite-likestrttctumasanoptimalprecursorforthepreparationofhydrogenationcatalysts(ref.1).Hydrotal
3、cite(amineralthatcanbeeasilycrushedintoawhitepowdersimilartotalc,discoveredinSwedenaround1842)isahydroxycarbonateofmagnesiumandaluminiumandoccursinnatureinfoliatedandcontortedplatesand/orfibrousmasses.Atthesametimethathydrotalcitewasdiscovered,anothermixedhydrox
4、ycarbonateofmagnesiumandironwasfound,whichwascalledpyroaurite(becauseofalikenesstogoldwhenheated)andwhichw,aslaterrecognizedtobeisostructuralwithhydrotalciteandothermineralscontainingdifferentelements,allofwhichwererecognizedashavingsimilarfeatures.Thefastexactf
5、ormulaforhydrotalcite,[Mg&l2(OH)16CO3.4H20],andoftheotherisomorphousmineralswaspresentedbyE.Manasse,professorofMineralogyattheUniversityofFlorence(Italy),whowasalsothefirsttorecognizethatcarbonateionswereessentialforthistypeofstructure(ref.2).Theopinioncurrentat
6、thattime,whichpersistedformanyyears,wasthatsuchmineralsweremixedhydroxides.OnthebasisofX-rayinvestigations,AminoffandBroome(ref.3)recognizedtheexistenceoftwopolytypesofhydrotalcite,thefirstonehavingrombohedralsymmetryandthesecondhavinghexagonalsymmetry,whichwasc
7、alledmanasseiteinhonourofManasse.ItwasnecessarytowaitforFrondelspaperpublishedin1941(ref.4),entitledConstitutionandPolymorphismofthePyroauriteandSjisgreniteGroupsbeforetheinterrelationsbetweentheseveralmineralsandtheirrealconstitutionsweregenerallyrecognized.The
8、confusionandtheuncertaintywereduetothelackofadequatecrystallographicdata,which,inturn,wasaresultofthecomplexandunusualcompositionofthesemineralsaswellasofthefactthatt
