Microemulsion and incipient wetness prepared Rh-based catalyst for diesel reforming

Abstract

The role of the catalyst preparation technique was investigated for diesel reforming. Reverse microemulsion (ME) and incipient wetness (IW) techniques were used for the preparation of Rh-based monolithic catalysts that were employed for hydrogen generation of low-sulfur diesel via autothermal reforming (ATR). The washcoat of the tested catalysts consisted of 0.5 wt% Rh, 1 wt% Rh, and 1:1 wt% Rh:Pt supported on γ-alumina. All washcoats were deposited on 400 cpsi cordierite monoliths. The reaction condition was T feed = 650 °C, H 2O/C ∼ 2.5, O 2/C ∼ 0.49, TOS = 3 h, GHSV ∼ 13 000 h −1 and P = 1 atm. Fresh and aged powder samples of the catalyst were characterized by N 2-BET, H 2 chemisorption, XRD, H 2-TPR, O 2-TPO and TEM. The activity results established that Rh and RhPt formulations, prepared by ME and IW, are highly active for ATR of diesel where fuel conversions above 92% were obtained. FTIR and NDIR analysis also showed that the highest formation of ethylene was found in the product gas stream from the bimetallic samples indicating that RhPt/Al 2O 3 is less resistant towards carbon deposition. The latter observation was confirmed by O 2-TPO analysis of the aged samples where high loads of coke were found both on the active metals and on the support. Interestingly, these effects were less significant on the ME samples. The characterization results clearly showed differences in morphology between the ME and the IW samples. N 2-BET analysis showed that higher surface area, ∼268–285 m 2/g, was obtained with the ME samples. Also, H 2 chemisorption analysis showed that the rhodium dispersion was ∼10% higher for the ME samples (H/Rh ∼ 60–66%). XRD analysis showed that crystalline phases of γ-alumina were present on all samples. The diffractograms also showed small traces of metallic Pt (∼16–30 nm) in the bimetallic samples. H 2-TPR analysis, showed peaks ascribed to bulk rhodium oxides and rhodium aluminates. It was also noted that the addition of Pt on the support lowered the reducibility of the different rhodium species. TEM analysis performed on the fresh and aged ME and IW bimetallic samples showed mainly Rh x Pt 1− x alloys with an average particle size of ∼20–50 nm were present on the alumina support. Also, for the aged samples, no sintering effects were noted. Furthermore, rhodium was found to switch oxidation state from e.g. Rh 3+ to Rh 0 while Pt remained in the metallic state.