TITLE: CO + H Sub 2 Reaction over Nitrogen-Modified Iron Catalysts. Final Technical Report, August 1, 1982-December 31, 1985.

AUTHOR: W. N. Delgass.

INST.  AUTHOR: Purdue Univ., Lafayette, IN. School of Chemical Engineering.

SPONSOR: Department of Energy, Washington, DC.

LANGUAGE: English

PUB.  TYPE: Technical Report

PUB.  COUNTRY: United States

SOURCE: Department of Energy [DE],  1985,  120p.

NTIS ORDER NO.: DE86014658/INW

ABSTRACT:

Our study of iron nitrides has included the preparation, stability, and catalytic kinetic behavior of these materials as Fischer-Tropsch synthesis (FTS) catalysts. Preparation of the three major phases ( gamma '-Fe sub 4 N, epsilon-Fe/sub x/N 2 < x < 3, zeta-Fe sub 2 N) is achieved by flowing NH sub 3 /H sub 2 mixtures over reduced iron powders in the temperature range 250 to 500 sup 0 C. The pure phases are easily identified by Moessbauer spectroscopy. Using constant velocity Moessbauer spectroscopy and mass spectral analysis we have (1) observed the expected fast decomposition of the nitrides in hydrogen, (2) shown that restricted access of hydrogen to the surface in the initial states of the decomposition can account for the low initial rate and the increase of the rate to a maximum, (3) show that the pure nitride phases are also very unstable in CO/H sub 2 at Fischer-Tropsch reaction conditions, but in the presence of CO-containing gases the nitrides are converted to carbonitrides rather than alpha -iron. Loss of nitrogen from the carbonitrides during reaction is a slow process. On the fresh surface, hydrogen reacts preferentially with nitrogen rather than CO, removing approximately one monolayer of nitrogen before methane production begins.  The carbonitrides formed after steady state reaction over the three iron nitride starting materials have been identified by Moessbauer spectroscopy. Kinetics of FTS at atmospheric pressure and 3/l H sub 2 /CO over these phases are reported. The activity and selectivity over iron nitrides are similar to those over reduced iron, although high initial activity, higher olefin to paraffin ratios, high CO sub 2 production rate and overall higher activity for the epsilon and zeta catalysts were noted for the nitrides. Pretreatment of nitrided catalysts with CO resulted in a momentary inhibition of all activity, whereas O sub 2 pretreatment gave evidence of enhanced C sub 4 selectivity. 44 refs., 30 figs., 13 tabs.  (ERA citation 12:003595)

REPORT  NUMBER: DOE/PC/50804-14

CONTRACT  NUMBER: FG22-82PC50804