Alkali-Poisoning-Resistant Fe₂O₃/MoO₃/TiO₂ Catalyst for the Selective Reduction of NO by NH₃: The Role of the MoO₃ Safety Buffer in Protecting Surface Active Sites

Abstract

The exhaust gas contains harmful products, including fuel-additive elements such as compounds of sodium, which cause dramatic catalyst deactivation of catalysts during selective catalytic reduction (SCR) of NO with NH3. There is an increasing demand to synthesize alkali-poisoning-resistant catalysts for industrial NH3-SCR applications. In this study, the as-synthesized Fe2O3/MoO3/TiO2 exhibits a high degree of resistance toward Na2SO4 poisoning during the NH3-SCR reaction. With 500 μmol g–1 Na+ poisoning, Fe2O3/MoO3/TiO2 showed approximately 95% (or more) of its original activity throughout the entire temperature rage. Even with 700 μmol g–1 Na+ poisoning, Fe2O3/MoO3/TiO2 still performed well. The 500 and 700 μmol g–1 Na+ loadings dictate that, on average, SCR catalysts could be exposed to alkali-rich and highly dusty environments for more than 14 000 and 20 000 h, respectively. The layered MoO3 building block is used as a binding buffer and sandwiched between the active phase and TiO2 support to provide sufficiently stable binding sites for Na2SO4 poison and to present alkali blocking of the surface active phase. Our findings provide useful information regarding the use of MoO3 as a safety buffer for developing functional NH3-SCR catalysts with enhanced alkali-poisoning-resistant performance and long lifetimes.

Iron-Based Composite Oxide Catalysts Tuned by CTAB Exhibit Superior NH3–SCR Performance

“…As shown in Figure 6, the peaks below 450 °C correspond to the reduction of Fe2O3 to Fe3O4. Further reduction of Fe3O4 to FeO and Fe occurred at higher temperatures (above 450 °C) [13,55,56]. Over the FeNb0.3Ox-C catalyst, it was observed that the peaks due to the reduction of Fe2O3 to Fe3O4 were centered at higher temperatures (348 °C and 413 °C) compared with FeNb0.3Ox (centered at 312 °C and 397 °C).…”

Molybdenum‐based heterogeneous catalysts for the control of environmental pollutants

“…Exhaust for NO x treatment often contains fuel‐additive alkali species, which cause 3–4 times acceleration in deactivation of commercial NH 3 ‐SCR catalysts 148 . Recently, quite a few researchers endorsed that MoO 3 displayed great assistance in alkali poisoning resistance 148,149 .…”

“…Exhaust for NO x treatment often contains fuel‐additive alkali species, which cause 3–4 times acceleration in deactivation of commercial NH 3 ‐SCR catalysts 148 . Recently, quite a few researchers endorsed that MoO 3 displayed great assistance in alkali poisoning resistance 148,149 . MoO 3 was described as “safety buffer” against Na 2 SO 4 poisoning in Fe 2 O 3 /MoO 3 /TiO 2 catalyst developed by Zhang et al 148 The mechanisms of V 2 O 5 ‐WO 3 /TiO 2 on Na + poisoning and Fe 2 O 3 /MoO 3 /TiO 2 on Na + poisoning resistance were illustrated in Figure 13(F).…”

Mechanistic studies on the conversion of NO gas on urea-iron and copper metal organic frameworks at low temperature conditions: in situ infrared spectroscopy and Monte Carlo investigations

“…Absence of NO 91( 23 (11) Upon inspecting the data in Table 2, it becomes clear that the maximum amount of NH 3 (g) produced in the presence of NO(g) was lower than that in the absence of NO(g) under dry and humid conditions for both M-BTC. These results suggest consumption of NH 3 (g) by NO(g) in the reduction reaction.…”

“…Given that the catalyst plays the crucial role in the NH 3 -SCR process, recent studies were focused on the improvement of the catalyst structure and operating conditions in order to boost their efficiency. 11 While ammonia has been extensively used as a reducing agent for the SCR reduction of NOx, urea has recently emerged as a more convenient option in terms of toxicity and hazard control. 12 Mina et al 13 studied the simultaneous effect of adding manganese oxide (Mn 2 O 3 ) and cobalt oxide (Co 3 O 4 ) along with the use of urea-SCR.…”