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Abstract: The influence of the nature and environmental of vanadium on the catalytic properties of V x SiBEA zeolite in selective catalytic reduction of NO with ammonia is investigated. Catalysts containing 1–7.5wt.% of vanadium were prepared by a two-step postsynthesis method which consists, in the first step, of dealumination of TEABEA zeolite to obtain SiBEA support and then, in the second step, of contacting the obtained material with an aqueous solution of NH4VO3 at pH 2.7. XRD and low temperature N2 sorption results show that full dealumination of parent TEABEA zeolite by nitric acid treatment as well as incorporation of vanadium atoms in the framework of SiBEA zeolite do not change the crystallinity of BEA zeolite. The presence of isolated pseudo-tetrahedral V(V) species for low V content and pseudo-tetrahedral and octahedral V(V) species for high V content is evidenced by diffuse reflectance UV–vis, Raman and TPR. The catalytic activity of V x SiBEA in selective catalytic reduction of nitric oxide with ammonia as reducing agent strongly depends on the nature and environmental of vanadium in BEA structure. The single site V1.0SiBEA catalyst with isolated pseudo-tetrahedral V(V) species is active in SCR of NO process, with maximum NO conversion about 60% at 773K and with very low selectivity toward undesired N2O. In contrast, V3.0SiBEA and, especially, V7.5SiBEA catalyst containing mainly extra-framework octahedral V(V) and vanadium oxide species are less active in SCR of NO process at higher temperature and big amount of N2O is observed in the product stream. [Copyright &y& Elsevier]

A goal of this work was to investigate the influence of the preparation procedure and activation conditions (reduction temperature and reducing medium: pure hydrogen (100% H2) or hydrogen-argon mixture (5% H2-95% Ar)) on the activity of Co-containing BEA zeolites in Fischer–Tropsch synthesis. Therefore, a series of CoBEA zeolites were obtained by a conventional wet impregnation (Co5.0AlBEA) and a two-step postsynthesis preparation procedure involving dealumination and impregnation steps (Co5.0SiBEA). Both types of zeolites were calcined in air at 500 °C for 3 h and then reduced at 500, 800 and 900 °C for 1 h in 100 % H2 and in 5% H2–95% Ar mixture flow. The obtained Red-C-Co5.0AlBEA and Red-C-Co5.0SiBEA catalysts with various physicochemical properties were tested in Fischer–Tropsch reaction. Among the studied catalysts, Red-C-Co5.0SiBEA reduced at 500 °C in pure hydrogen was the most active, presenting selectivity to liquid products of 91% containing mainly C7–C16 n-alkanes and isoalkanes as well as small amount of olefins, with CO conversion of about 11%. The Red-C-Co5.0AlBEA catalysts were not active in the Fischer–Tropsch synthesis. It showed that removal of aluminum from the BEA zeolite in the first step of postsynthesis preparation procedure played a key role in the preparation of efficient catalysts for Fischer–Tropsch synthesis. An increase of the reduction temperature from 500 to 800 and 900 °C resulted in two times lower CO conversion and a drop of the selectivity towards liquid products (up to 62%–88%). The identified main liquid products were n-alkanes and isoalkanes. The higher activity of Red-C-Co5.0SiBEA catalysts can be assigned to good dispersion of cobalt nanoparticles and thus a smaller cobalt nanoparticles size than in the case of Red-C-Co5.0AlBEA catalyst. [ABSTRACT FROM AUTHOR]

Cu x SiBEA zeolites (with x = 1–7.5 Cu wt %) prepared by a two-step postsynthesis method which consists in the first step of dealumination of parent BEA zeolite to obtain aluminum-free SiBEA support and then in the second step, of contacting the obtained material with an aqueous solution of copper nitrate, were used in this work as catalysts of SCR of NO with ammonia. XRD, TPR and FTIR investigations showed that up to 2 wt % of Cu was successfully incorporated into zeolite beta structure as framework mononuclear Cu(II). The FTIR of pyridine sorption revealed that the incorporation of copper into zeolite framework led to the creation of new Lewis acidic sites which were responsible for high activity of Cu x SiBEA zeolite catalysts in SCR of NO with ammonia. The catalytic activity of Cu x SiBEA in SCR of NO with ammonia used as a reducing agent strongly depends on the nature and environmental of copper in BEA structure. The Cu 1.0 SiBEA catalyst with predominantly framework Cu(II) was the most active and selective among the tested samples in wide temperature range. In contrast, the application of Cu x SiBEA zeolite catalysts with higher Cu content (>than 2 wt % of Cu) containing a mixture of framework and extra-framework Cu(II) resulted in low NO conversion in SCR at high temperature range, as well as, the high concentration of undesired N 2 O in outgas stream. It indicates that octahedral Cu(II) and/or copper oxides present in extra-framework position of SiBEA zeolite promote at high temperature ammonia oxidation. [ABSTRACT FROM AUTHOR]

The influence of cobalt environment on the catalytic properties of Co x SiBEA zeolite in selective catalytic reduction of NO with ammonia was studied. Catalysts were prepared by a two-step postsynthesis method which consists, in the first step, of dealumination of parent BEA zeolite to obtain aluminum-free SiBEA support and then, in the second step, of contacting the obtained material with an aqueous solution of cobalt nitrate. DR UV–Vis and XPS results showed that cobalt was successfully incorporated into zeolite beta framework as isolated mononuclear Co(II). The presence of only isolated framework mononuclear Co(II) was evidenced in Co x SiBEA with cobalt content lower than 2 wt % and both isolated framework mononuclear Co(II) and extra-framework octahedral Co(II) for Co 3.0 SiBEA catalyst. FTIR investigation of pyridine adsorption revealed that the incorporation of cobalt into zeolite framework led to a creation of new Lewis acidic sites which are responsible for high activity in SCR of NO with ammonia. The catalytic activity of Co x SiBEA in selective catalytic reduction of NO with ammonia as reducing agent strongly depends on the nature and environment of cobalt in BEA structure. The single-site Co 2.0 SiBEA zeolite catalyst was the most active among tested, with maximum NO conversion about 80% at 673 K. In contrast, Co 3.0 SiBEA catalyst containing a mixture of framework and extra-framework Co(II) had lower activity in SCR of NO process than Co 2.0 SiBEA at higher temperature due to a competitive reaction of ammonia oxidation to NO. [ABSTRACT FROM AUTHOR]

An integrated experimental and computational study was carried out on molybdenum loaded BEA zeolite in order to scrutinize the most stable state of the molybdenum site at various oxidation and hydration states. After a two-step post-synthetic process, the incorporation of Mo ions into the vacant T-atom sites of the SiBEA framework zeolite as mononuclear Mo VI centers has been evidenced by combined use of XRD, FTIR and diffuse reflectance UV–vis spectroscopy. The consumption of OH groups upon Mo loading has been monitored by FTIR and adsorbed pyridine is used as probe molecules for characterization of Brønsted and Lewis acidity in SiBEA and Mo 3.0 SiBEA. Periodic DFT calculations in sodalite (SOD) framework indicate a trigonal-bipyramidal conformer at the Mo VI site with molybdenum being incorporated into the zeolite framework by four SiO– bonds and a Mo O functionality under anhydrous conditions. Water splitting formally to O 2− and 2H + is computed to be feasible in SOD cage, whereas it is strongly favored in MoBEA framework at the T1 position. Depending on the hydration state, it is shown that the Mo sites formed can exhibit two Mo O functionalities in a trigonal-bipyramidal and a pseudo-octahedral arrangement. [ABSTRACT FROM AUTHOR]

Abstract: Two series of V x SiBEA(I) and V x SiBEA(II) zeolites have been prepared by a two-steps postsynthesis method which consists, in the first step, in the dealumination of TEABEA zeolite by two different procedures to obtain SiBEA(I) and SiBEA(II) zeolites and then, in the second step, in contacting the obtained zeolites with an aqueous NH4VO3 solution at pH 2.7. Because the NH4VO3 solution at pH 2.7 predominantly contains mononuclear VO2 + ions, vanadium can be incorporated into SiBEA(I) and SiBEA(II) as framework pseudo-tetrahedral non hydroxylated (SiO)3V(V)roxylated (SiO)2(OH)V(V) by reaction with silanol groups of vacant T-atom sites. Combined use of FTIR, DR UV–vis, 51V NMR, EPR and TPR allows to determine the oxidation state, nature and environment of vanadium in as prepared, calcined, rehydrated, activated and reduced V x SiBEA(I) and V x SiBEA(II) samples. It is shown that the procedure of dealumination has the effect on the properties of the silanol groups of vacant T-atom sites in SiBEA(I) and SiBEA(II) and on the nature and environment of V species in as prepared V x SiBEA(I) and V x SiBEA(II). As evidenced by DR UV–vis and 51V MAS NMR in V x SiBEA(II), vanadium is present only as pseudo-tetrahedral V(V) species, and in contrast in V x SiBEA(I) as pseudo-tetrahedral and octahedral V(V) species. The oxidation state of framework tetrahedral vanadium in V x SiBEA(I) and V x SiBEA(II) easily change upon calcination in oxygen, outgassing at 773K and reducing with hydrogen at high temperature (873K), as shown by EPR. The presence of Brønsted and Lewis acidic centres are evidenced in V x SiBEA(II) by FTIR adsorption investigations of pyridine and CO used as probe molecules. [Copyright &y& Elsevier]

Abstract: The influence of the state of iron on the catalytic properties of Fe x SiBEA zeolite in the oxidation of CO was investigated. Various Fe x SiBEA zeolites (x =0.6, 1.0, 4.0 and 10wt%) were prepared by a two-step post synthesis method. The presence of Fe(III) in tetrahedral coordination for low Fe content and tetrahedral and octahedral coordination for high Fe content is evidenced by diffuse reflectance UV–Vis and TPR. FTIR investigations of pyridine adsorption show that Brønsted and Lewis acidic sites are formed upon incorporation of iron in SiBEA zeolite. The amount of both acidic sites increases with Fe content. The catalytic activity of Fe x SiBEA in the oxidation of CO strongly depends on the state of iron in BEA structure. Fe0.6SiBEA and Fe1.0SiBEA containing mainly framework tetrahedral Fe(III) ions are more active than Fe10SiBEA containing mainly extra-framework FeO x oligomers. The most active catalyst is Red-Fe1.0SiBEA obtained after reduction of Fe1.0SiBEA at 760°C in flowing H2. It shows almost 100% CO conversion at room temperature. [Copyright &y& Elsevier]