Abstract: The invention concerns a process for skeletal isomerisation of linear olefins using a catalyst containing at least one pre-treated molecular sieve selected from the group formed by SAPO-31, SAPO-11, Theta-1, EU-1, omega zeolite, mordenite, Nu-10, Nu-86, Nu-87, ferrierite, ZSM-12 and ZSM-23.

Abstract: The invention concerns a process for skeletal isomerization of linear olefins using a catalyst containing at least one pre-treated molecular sieve selected from the group formed by SAPO-31, SAPO-11, Theta-1, EU-1, omega zeolite, mordenite, Nu-10, Nu-86, Nu-87, ferrierite, ZSM-12 and ZSM-23. The pre-treatment process consists in bringing the molecular sieve, which has a pore size of 0.4 to 0.8 nm, into contact with at least one hydrocarbon molecule containing 4 to 20 carbon atoms, at a space velocity of 0.1-45 h.sup.-1, a temperature of 300.degree.-550.degree. C. and at a pressure of 0.1-1 MPa, for 0.5-48 h, to deposit coke in the pores. The process is of particular application to one-dimensional sieves. It is preferably carried out outside the reaction zone. The invention also concerns a catalyst containing a pre-treated sieve, the sieve being selected from SAPO-31, SAPO-11, Theta-1, EU-1, omega zeolite, mordenite, ferrierite, Nu-10, Nu-86 and Nu-87.

Abstract: The invention concerns a new process for the production of primary and secondary mercaptans.The invention is based on the fact that it is possible to cause an hydrogen exchange between a thioaldehyde or a thioketone and a mercaptan with very good selectivity and conversion yields.

Abstract: Preparation of a thiophene by the action of H.sub.2 S on an organic substance containing oxygen or sulphur.The substance which is used is an unsaturated carbonyl or thiocarbonyl compound, particularly an aldehyde, thioaldehyde, ketone or thioketone. The reaction preferably takes place between 250.degree. and 500.degree. C. on a catalyst of the alumina type containing an alkali or alkaline earth oxide.The process permits the unsubstituted or substituted thiophene to be obtained with high yields and high degrees of selectivity, exceeding 70%.