Synthesis of Zeolitic Ti, Zr-Substituted Vanadotungstates and Investigation of Their Catalytic Activities for Low Temperature NH₃-SCR

Abstract

Microporous vanadotungstate (W 4 V 3 O 19 , VT-1) was constructed via the connection of [W 4 O 16 ] 8− cubane units with VO 2+ linkers to form an LTA-zeolite-type crystal structure. We found that the VO 2+ sites connecting the cubane units of VT-1 could be partially removed by an appropriate acid treatment without destroying its crystal structure. This process involved a redox reaction between the [W 4 O 16 ] 8− cubane units and VO 2+ linkers, and V was removed as V 5+ during the acid treatment. TiO 2+ or ZrO 2+ could be introduced into the VO 2+ vacancies. The introduction of Ti or Zr substantially improved the thermal stability of VT-1 under oxidizing conditions. The catalytic activity toward the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) was improved by the introduction of Ti or Zr.

Investigation of the Synthesis of Zeolitic Vanadotungstate and its Use in the Separation of Propylene/Propane at High Temperature and Humidity

“…The chemical formulae of Cu-VT-1 , Zn-VT-1 , and Mn-VT-1 were estimated to be Cu­[W 4 V 3 O 19 ], H 1.4 Zn 1 [W 4 Zn 0.7 V 2.3 O 19 ], and Mn 1.3 [W 4 V 3 O 19.3 ], respectively. For Zn-VT-1 , Zn might also be replaced with some V, which was also observed when using Ti and Zr ions for ion exchange . NH 4 + exchange was carried out for Zn-VT-1 (see the Supporting Information for details), and the structure did not change (Figure S6).…”

“…For Zn-VT-1, Zn might also be replaced with some V, which was also observed when using Ti and Zr ions for ion exchange. 43 NH 4 + exchange was carried out for Zn-VT-1 (see the Supporting Information for details), and the structure did not change (Figure S6). The elemental analysis of the resulting material showed that Zn still existed in the material (Zn content of 1.31%) after NH 4 + exchange, indicating that some Zn 2+ was incorporated into the framework.…”

Microporosity and Catalytic Activity for Hydrodesulfurization of Pharmacosiderite Mo4P3O16 Synthesized at a Moderate Temperature

“…At that time, the O–H distance between NH 4 + and CO 2 was reasonable and was 2.53–2.78 Å after the geometry optimization, and the adsorption energy of E CO2 = −62 kJ mol –1 CO2 was obtained (Figure d). There are a few examples of microporous materials composed of transition-metal elements in an all-inorganic manner. − These properties could offer versatile applications due to the microporous structure and redox properties.…”

“…Recently, a new class of microporous materials composed of d-block elements, namely, zeolitic octahedral metal oxides (ZOMOs), has been reported, and applications derived from their redox-active constituents and microporosity are being developed. However, ZOMOs are still rare, although much effort has been devoted to their synthesis. − …”

Redox-induced control of microporosity of zeolitic transition metal oxides based on ε-Keggin iron molybdate at an ultra-fine level

“…26 Crystalline microporous transition metal oxides composed of metal-oxygen octahedra are assembled by metal oxygen clusters as building units and metal ions as linkers, and therefore the materials are also called zeolitic octahedral metal oxides (ZOMOs). [27][28][29][30] Various ZOMOs have been reported in recent years, such as pentagon unit-based vanadomolydates, [31][32][33][34] hexagonal unit-based cobalt selenotungstate, 35 cubane unit-based vanadotangstate, 30,36,37 and ε-Keggin polyoxometalate (POM) unit-based molybdates. 29,38,39 Among these ZOMOs, the ε-Keggin unit-based molybdates (Fig.…”