Supported Tantalum Oxide and Supported Vanadia-tantala Mixed Oxides: Structural Characterization and Surface Properties

Abstract

Silica-, alumina-, and zirconia-supported tantalum oxide and supported vanadia-tantala mixed oxide catalysts were investigated by XRD, UV-vis-DR, FTIR, and FT-Raman spectroscopy to determine the nature of the surface tantala species. Two types of surface TaO x species were identified. On the SiO 2 support, at low coverages tetrahedral TaO 4 species exist, with a TadO bond and three bridging Ta-O-support bonds. At higher coverages, octahedral TaO 6 species occur. On Al 2 O 3 and ZrO 2 both surface species exist already at considerably low Ta loading. The acidic properties of the catalysts were investigated by an FTIR study of adsorbed pyridine. Supported tantala is clearly more Lewis acidic in comparison to vanadia. The oxidation of methanol was used to probe the catalytic performance of the supported oxide species and from the activity and product distribution it is concluded that supported tantala predominantly shows acidic over redox behavior.

Use of Oxide Ligands in Designing Catalytic Active Sites

“…Therefore, monolayer coverage or maximum dispersion limit is a critical parameter that allows distinguishing between two-dimensional molecularly dispersed surface metal oxide species and the three-dimensional NPs present in supported metal oxide materials. For the purposes of simplifying and focusing the discussion, only SiO 2 -supported metal oxide catalysts at submonolayer coverages will be discussed in this chapter since the catalysis literature has demonstrated that only isolated surface metal oxide species are present at low coverage for supported MO x /SiO 2 catalysts [14,[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56].…”

Síntese, caracterização e avaliação das propriedades catalíticas de VOx/Ta2O5-Al2O3 para a reação de decomposição do isopropanol

“…Alguns óxidos de metais do grupo V, como tântalo e vanádio, e óxido de alumínio USHIKUBO;WADA, 1995;BALTES et al, 2001;ARGYLE et al, 2004;MARTINEZ-HUERTA et al, 2006;CORTEZ et al, 2003) vêm sendo estudados em busca de uma melhor performance. (LIETTI et al, 1999).…”

“…O catalisador ternário vanadiatântala-suporte é potencialmente útil em reações que necessitem tanto de sítios ácidos como redox (BALTES et al, 2001). …”

“…Atualmente, a principal matéria-prima para a produção de alumina é a bauxita, BALTES et al, 2001;WACHS et al, 2003).…”

“…Óxido de tântalo é utilizado como revestimento ótico ou como material capacitor, devido à sua alta constante dielétrica (KUKLI et al, 2000;POLLARD;PUDDEPHATT, 1999) distorcida quando a cobertura superficial é média ou alta (TANAKA et al, 1999;CHEN et al, 2003;BALTES et al, 2001). Análises de espectroscopia Raman revelaram que o óxido de tântalo possui apenas uma ligação Ta=O terminal e de 3 a 5…”