The Question of Artificial Photosynthesis of Ammonia on Heterogeneous Catalysts

The Role of Adventitious Carbon in Photo-catalytic Nitrogen Fixation by Titania

“…This hypothesis is consistent with prior reports of carbon radical formation, − the role of surface carbon contaminants in photo-catalysis, spin-mediated N 2 adsorption, and strong interactions between nitrogen and graphene edges . The hypothesis is also consistent with a number of key observations in the nitrogen photo-fixation literature including the correlation of rate with oxygen vacancies , and sacrificial reagents, ,, the detrimental effect of gas-phase oxygen, and the large variations and inconsistencies in measured rates for catalysts that are nominally identical. ,, The findings indicate that careful characterization and control of surface carbon is critical to ensure reproducibility in photo-catalytic nitrogen fixation on titania and other semiconductors, and suggest that engineering carbon-based active sites is a promising strategy for enhancing photo-catalytic nitrogen fixation.…”

“…Photo-generation of ammonia by titania-based catalysts has been reported by numerous independent groups since, including with more controlled techniques such as isotopic labeling; ,, however, the influence of hydrocarbons was neglected. There are also considerable discrepancies in the literature and open questions regarding the thermodynamics that drive the process. ,, Given the recent explosion of interest in this field, it is critical to establish hypotheses about the active site and reaction mechanism that resolve these inconsistencies …”

Preparation of iron catalysts for NOx removal from the tail gas of HNO3 plants

“…The absorption edge in the region from 400 to 600 nm can be assigned to the 6 A 1 → 4 T 2 (4G) ligand field transition of high spin Fe 3+ ion in tetrahedral structure. The mention bands corresponding to d-d transition and the band gap values in adsorption edge for M/ Fe/ NaY catalysts (M = alkali or alkali earth metal ions) were lower than that of bulk iron (III) oxide α-Fe 2 O 3 (2.1 eV expect in Ce/ Fe/NaY) and higher than Fe/ NaY (1.8 eV) in this experimental and correspond to the literature [22,23]. The adsorbed NH 3 be activated by Fe 3+ ion and the mention promoters promotes NO adsorption in the octahedral sites.…”

Analysis of Photocatalytic Nitrogen Fixation on Rutile TiO2(110)

“…It was shown that dinitrogen can be converted to ammonia under both aqueous conditions , and humidified air, , with higher rates observed in gas-phase conditions . Further, the titania photocatalysts selectively reduce nitrogen to ammonia in most studies, ,,− , although some work indicates that oxidation to nitrates occurs, , and other authors observed no photocatalytic nitrogen fixation activity. − In addition, the presence of the rutile crystal phase and iron dopants were found to be critical for enhancing nitrogen reduction activity. ,,, The iron dopants have been proposed to promote the formation of rutile domains, and/or enhance separation of charge carriers by acting as an electron sink; while the exact role is not known, the prevailing hypothesis is that Fe is not part of the active site based on the observation that excess Fe content reduces catalytic activity . More recently, the solar-to-ammonia efficiency was measured to be around 0.02% for a pure titania sample, and the authors hypothesize that the reaction occurs via direct N–N bond scission at a rutile (110) bridging oxygen-vacancy (O-br) active site .…”