Ammonia-Assisted Light Alkane Anti-coke Reforming on Isolated ReO_x Sites in Zeolite

Abstract

The conventional reforming produces H 2 with stoichiometric amounts of CO and CO 2 from hydrocarbons. Here, we show that CO x -free H 2 can be produced from ammoniaassisted reforming (ammoreforming) of natural gas liquids (C n H 2n+2 + nNH 3 = nHCN + (2n + 1) H 2 , n = 2 or 3) at the same conditions as the steam reforming. Such a process coproduces HCN, which can be easily separated from H 2 and used as value-added chemicals or for NH 3 recycling through hydrolysis. The ammoreforming of ethane and propane was realized over the Re-modified HZSM-5 zeolite rather than the traditional Pt-based catalyst for the BMA process (methane ammoreforming). The specific activity of the Re/HZSM-5 catalysts at 650 °C is up to 1 mol H 2 /g Re /min (or 180 min −1 ) during ethane ammoreforming. The catalyst is highly coke resistant and shows only slight deactivation with a time-on-stream up to 20 h. Characterization of the fresh and used catalysts by X-ray absorption and Raman spectroscopies suggested that the isolated ReO x site grafted by AlO 4− tetrahedral in the zeolite framework is responsible for the outstanding catalytic activity and coke resistibility. KEYWORDS: light alkanes, ammonia reforming, anti-coke, isolated ReO x , CO x -free H 2

Ammonia-assisted reforming and dehydrogenation toward efficient light alkane conversion

“…While the conventional Degussa BMA process requires a high reaction temperature of ≥1200 °C, more recent studies show that the AmmoReform of light alkanes (ethane and propane from natural gas liquid) can be achieved at 600–700 °C. 58 This result demonstrated the possibility of achieving AmmoReform at relatively low temperatures (the same reaction temperature as the SteamReform and dry reforming processes). The efficient low-temperature AmmoReform of ethane and propane was realized over the Re-modified HZSM-5 zeolite rather than the conventional Pt-based catalyst for the BMA process.…”

“…In order to understand the structure of Re species in HZSM-5 zeolite, the catalyst has been extensively characterized by X-ray absorption spectroscopy at Re L III -edge, in situ Raman spectroscopy, and HAADF-STEM. 58 The formation of ReO 4 − tetrahedra (see Fig. 6(d)), anchored to the framework Al f O 4 − (Al–O f − –Si) by replacing the Brønsted acid site in the 10MR (10-membered ring) of the ZSM-5 zeolite, was expected for the fresh catalyst.…”

“…The concept of ammonia reforming (AmmoReform) for light alkane upgradation for CO x -free H 2 production was recently proposed by our group. 58 Such a catalytic process is closely related to the BMA and Shawinigan processes in terms of the reaction stoichiometry. Taking ethane AmmoReform as an example, the stoichiometric reaction is shown in eqn (1).…”

“…Without Re, pure HZSM-5 shows <1.5% ammonia conversion (through decomposition) and negligible ethane conversion under the same reaction conditions. 58…”

Experimental Evidence for Alloying Effects in Au–Pt-Catalyzed Low-Temperature CH4Activation with NO

“…The main body of literature on CH 4 functionalization to HCN is of studies of CH 4 –NH 3 coupling with or without O 2 at temperatures above 1000 °C, − and only a few papers have dealt with reactions at much lower temperatures. Among these, Yi and co-workers have reported HCN TOF values of 17.6 h –1 on Pt/titanosilicate zeolite (GHSV = 8 730 000 h –1 ) and 9.6 h –1 on Cu/silicalite-1 catalysts (GHSV = 1529 h –1 ) through a plasma-assisted CH 4 /NH 3 process at 400 °C, , while Xiang and co-workers have reported a maximum HCN TOF of 2856 h –1 on Re/HZSM-5 catalysts via ammonia-assisted reforming of ethane at 650 °C (GHSV = 6600–133 000 h –1 ) . In the present work, a maximum HCN TOF of 740 h –1 was obtained during contact time measurement on 1Au5Pt/Al 2 O 3 at 400 °C (GHSV = 11 300 h –1 ), showing that the CH 4 /NO reaction compares favorably with reported works on the basis of turnover frequency.…”