Production process of propylene

1. A process of producing propylene comprising contacting ethylene with a catalyst to form propylene, wherein:

the catalyst comprises a zeolite as an active ingredient;

an acid content in the outer surface of the zeolite is 5% or less based on an acid content of the entire zeolite;

the acid content in the outer surface is measured by allowing a substance, capable of selectively adsorbing on acid sites of the zeolite and incapable of intruding into the inside of a micropore of the zeolite, to adsorb on the zeolite, and quantitatively determining the adsorption amount;

the acid content of the entire zeolite is measured by allowing a substance, capable of selectively adsorbing on acid sites of the zeolite and intruding also into the inside of the micropore, to adsorb on the zeolite, and quantitatively determining the adsorption amount; and said zeolite has a pore size of less than 0.5 nm.

2. The process of claim 1 , wherein said acid content in the outer surface of the zeolite is represented by a pyridine desorption amount defined by the following (I):

(I) a pyridine desorption amount per zeolite unit weight at 150 to 800° C. measured by a temperature-programmed desorption method at a temperature rising rate of 10° C./min on a pyridine-adsorbing zeolite that is obtained by drying a zeolite in vacuum at 500° C. for 1 hr as a pretreatment, contacting the pretreated zeolite with pyridine vapor at 150° C. to adsorb pyridine on the zeolite, and removing excess pyridine from said zeolite at 150° C. by exhausting under decompression and a helium flow.

3. The process of claim 1 , wherein said acid content of the entire zeolite is represented by an ammonia desorption amount defined by the following (II):

(II) an ammonia desorption amount per zeolite unit weight at 100 to 800° C. measured by a temperature-programmed desorption method at a temperature rising rate of 10° C./min on an ammonia-adsorbing zeolite that is obtained by drying a zeolite under an a helium flow at 500° C. for 1 hr as a pretreatment, contacting the pretreated zeolite with 5 vol% ammonia/helium at 100° C. to adsorb ammonia on the zeolite, and contacting the obtained zeolite with steam at 100° C. to remove excess ammonia from said zeolite.

4. The process of claim 1 , wherein said zeolite has an oxygen 8-membered ring structure or an oxygen 9-membered ring structure.

5. The process of claim 1 , wherein a framework structure of said zeolite is a CHA structure.

6. The process of claim 1 , wherein the outer surface of said zeolite is silylated.

7. The process of in claim 1 , wherein said zeolite is steam-treated.

8. The process of claim 7 , wherein a temperature of said steam treatment is from 400 to 700° C.

9. The process of claim 7 , wherein said zeolite is steam-treated after mixing with a compound containing an alkaline earth metal.