The present invention provides an improved etchant composition and method for the resistivity specific etching of doped silicon films which overlie intrinsic or lightly doped crystal regions. The composition of the etchant is 0.2-6 mole % hydrofluoric acid, 14-28 mole % nitric acid, and 66-86 mole % acetic acid/water. The etchant leaves no silicon residue and provides for controlled etching with an etch stop at the lightly doped or intrinsic region.

There is provided a catalyst comprising a zeolite component and a microcrystalline, microporous aluminum phosphate component. Examples of the zeolite component are ZSM-5 and zeolite Beta, and an example of an aluminum phosphate component is AlPO.sub.4 -5. The aluminum phosphate component provides increased catalyst activity and lifetime. Also provided for in this disclosure are a method for making the zeolite/aluminum phosphate composite and a process for using this composite in the preparation or conversion of hydrocarbons, e.g., in a dewaxing process.

Cracking catalysts and their use in cracking processes are disclosed. The cracking catalyst are prepared using mixtures of catalytic cracking catalysts containing zeolitic aluminosilicates effective in catalytic cracking and selected silicoaluminophosphate molecular sieves of U.S. Pat. No. 4,440,871.

The present invention relates to a process for catalytically dewaxing a hydrocarbon oil feedstock by contacting the feedstock with a combination of a catalyst comprising an intermediate pore size silicoaluminophosphate molecular sieve and a hydrogenation component and an intermediate pore size aluminosilicate zeolite catalyst.

An novel class of iron-aluminum-phosphorus-silicon-oxide molecular sieves is disclosed which contain as framework constituents FeO.sub.2.sup.-, and/or FeO.sub.2.sup.-2, AlO.sub.2.sup.-, PO.sub.2.sup.+ and SiO.sub.2 tetrahedral oxide units. These compositions are prepared hydrothermally, preferably using organic templating agents and are suitably employed as adsorbents and catalysts.