Preparation, and characterisation and catalytic activity of acid-activated organoclays.

Three montmorillonites SWy-2 (Wyoming, USA), STx-1 (Texas, USA) and SAz-1 (Cheto, Arizona, USA) and one saponite Sap-Ca (California, USA) were treated with different amounts of 12 M HCl and 1 M tetramethylammonium (TMA[+]) solution. The catalysts were characterised by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The catalytic activity of these acid-activated organoclays (AAOCs) was measured using the isomerisation of a-pinene at 120 &deg;C for 1 h to yield camphene and limonene and compared to clays acid-treated in the absence of TMA[+]. The total conversion for the isomerisation was excellent for AAOCs formed from SWy-2 (88%) and STx-1 (73%), moderate for Sap-Ca (50%) and low for SAz-1 (20%). Samples treated alone with TMA[+] did not exhibit any marked catalytic activity, which reached an optimum at intermediate TMA+-loadings. Acid-treated Sap-Ca and STx-1, which contained no TMA[+] cations were also effective catalysts for the isomerisation process. TMA[+] cations were unexpectedly resistant to exchange by protons. The same clays were activated with aluminium and TMA[+] to obtain materials with a combined Al[3+] and TMA[+] content equal to their CECs. The number of acid sites was measured using the thermal desorption of cyclohexylamine and the catalytic activity was evaluated using the same test reaction and compared to clays in absence of TMA[+]. A reduction in both acidity and catalytic activity was observed in samples activated with an Al:TMA ratio < 0.66. The activity of the catalysts remained almost constant for the overall conversion when the aluminium content was >70% in either the presence or absence of TMA[+]. The total conversion followed the order Sap-Ca > STx-1 > SWy-2 > SAz-1 in both samples treated with Al[3+] and Al[3+]/TMA[+]. Aluminium activated organoclays using divalent organocations (1,4-diazabicyclo[2.2.2]octane (DABCO) and 1,5-diaminopentane (DAP)) were also prepared from SWy-2 to compare the activity with those obtained using TMA[+]. The order of activity was Al/TMA > Al/DABCO > Al/DAP. The increment in the Al content did not cause a significant effect on the activity. The acidity of these samples was given by protons arising from different equilibria. SWy-2, Sap-Ca and SAz-1 were ion-exchanged (IECs) with different cations (Al, Ca, Mg, Na and Ni) using various exchange treatments. It was found that the exchange treatment had a marked influence upon the total conversion of a-pinene. The order of activity for IECs was Al > Ni > Mg > Ca > Na, with Sap-Ca being more active than SWy-2 and SAz-1. Aluminium activated clays and organoclays derived from STx-1 were saturated with hept-1-ene. The samples were heated and the gases evolved analysed by FTIR and GC-MS. Hept-1-ene reacted with the clays via proton transfer and resulted in the formation of a variety of reaction products (more than 60 hydrocarbons). TMA[+] cations reduced the population of protons to selectively produce isomerisation and hydration products. The thermal stability of four clays [JP (montmorillonite, Jelsovy Potok, Slovakia), SAz-1 (montmorillonite, Cheto, Arizona, USA), ST (beidellite, Stebno, Czech Republic) and SWa-1 (montmorillonite, Washington, USA)] in the Na- and autotransformed (An)-forms were exchanged with alkylammonium ions of variable chain lengths. The Na-organoclays were more resistant to thermal decomposition than for An-organoclays derived from SAz-1, JP and ST, but not for SWa-1 in which both series of samples had similar thermal behaviour. The weight loss registered for An-organoclays was higher than for Na-organoclays. TG-FTIR revealed the organoclays underwent thermal decomposition to produce ammonia, aliphatic hydrocarbons, CO[2] and water.