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align=center><A name=OLE_LINK2><STRONG><SPAN lang=ES-AR
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size=3>Seminarios del Dpto. de Química Inorgánica, Analítica y Química Física /
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Universidad de Buenos Aires</SPAN></STRONG></SPAN><SPAN
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href="http://www.qi.fcen.uba.ar/es"><FONT size=3><SPAN
style="mso-bookmark: OLE_LINK2"><B><SPAN lang=ES-AR
style="FONT-FAMILY: Arial; mso-ansi-language: ES-AR">http://www.qi.fcen.uba.ar/es</SPAN></B></SPAN><SPAN
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lang=PT-BR
style="COLOR: black; FONT-FAMILY: Arial; mso-ansi-language: PT-BR">2do.
Cuatrimestre, 2006</SPAN></STRONG></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=PT-BR
style="FONT-FAMILY: Arial; mso-ansi-language: PT-BR"><o:p></o:p></SPAN></SPAN></FONT></P>
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align=center><SPAN style="mso-bookmark: OLE_LINK2"><STRONG><SPAN lang=PT-BR
style="FONT-SIZE: 14pt; COLOR: black; FONT-FAMILY: Arial; mso-ansi-language: PT-BR">Lunes
13 de Noviembre, 13.00h</SPAN></STRONG></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><B><SPAN lang=PT-BR
style="COLOR: black; FONT-FAMILY: Arial; mso-ansi-language: PT-BR"><BR><STRONG><SPAN
style="FONT-FAMILY: Arial"><FONT size=3>Aula Seminarios, DQIAyQF-
INQUIMAE<o:p></o:p></FONT></SPAN></STRONG></SPAN></B></SPAN></P>
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lang=ES-AR
style="COLOR: black; FONT-FAMILY: Arial; mso-ansi-language: ES-AR">Ciudad
Universitaria, Pab. II, Piso 3</SPAN></STRONG></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><B><U><SPAN
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align=center><SPAN style="mso-bookmark: OLE_LINK2"><SPAN lang=FR
style="FONT-SIZE: 14pt; FONT-FAMILY: Arial; mso-ansi-language: FR"><o:p> </o:p></SPAN></SPAN></P>
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align=center><SPAN style="mso-bookmark: OLE_LINK2"><B
style="mso-bidi-font-weight: normal"><SPAN lang=FR
style="FONT-SIZE: 16pt; FONT-FAMILY: Arial; mso-ansi-language: FR">Eric M.
Gaigneaux<o:p></o:p></SPAN></B></SPAN></P>
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align=center><SPAN style="mso-bookmark: OLE_LINK2"><SPAN lang=FR
style="FONT-FAMILY: Arial; mso-ansi-language: FR"><FONT size=3>Université
catholique de Louvain, Unité de catalyse et chimie des matériaux
divisés,<o:p></o:p></FONT></SPAN></SPAN></P>
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align=center><SPAN style="mso-bookmark: OLE_LINK2"><SPAN lang=FR
style="FONT-FAMILY: Arial; mso-ansi-language: FR"><FONT size=3>Croix du Sud
2/17, B-1348 Louvain-la-Neuve (Belgium).<o:p></o:p></FONT></SPAN></SPAN></P>
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align=center><FONT size=3><SPAN style="mso-bookmark: OLE_LINK2"><SPAN lang=PT-BR
style="FONT-FAMILY: Arial; mso-ansi-language: PT-BR">E-mail: </SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"></SPAN></FONT><A
href="mailto:gaigneaux@cata.ucl.ac.be"><FONT size=3><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=PT-BR
style="COLOR: windowtext; FONT-FAMILY: Arial; TEXT-DECORATION: none; mso-ansi-language: PT-BR; text-underline: none">gaigneaux@cata.ucl.ac.be</SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"></SPAN></FONT></A><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=PT-BR
style="FONT-FAMILY: Arial; mso-ansi-language: PT-BR"><FONT size=3> - Tel:
+32(0)10-473649 – Fax: +32(0)10-473665<o:p></o:p></FONT></SPAN></SPAN></P>
<P class=MsoBodyText style="MARGIN: 0cm -7.2pt 0pt 0cm; TEXT-ALIGN: center"
align=center><SPAN style="mso-bookmark: OLE_LINK2"><B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US
style="FONT-SIZE: 14pt; FONT-FAMILY: Arial; mso-ansi-language: EN-US"><o:p> </o:p></SPAN></B></SPAN></P>
<P class=MsoBodyText style="MARGIN: 0cm -7.2pt 0pt 0cm; TEXT-ALIGN: center"
align=center><SPAN style="mso-bookmark: OLE_LINK2"><B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US
style="FONT-SIZE: 14pt; FONT-FAMILY: Arial; mso-ansi-language: EN-US"><o:p> </o:p></SPAN></B></SPAN></P>
<P class=MsoBodyText style="MARGIN: 0cm -7.2pt 0pt 0cm; TEXT-ALIGN: center"
align=center><SPAN style="mso-bookmark: OLE_LINK2"><B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US
style="FONT-SIZE: 14pt; FONT-FAMILY: Arial; mso-ansi-language: EN-US">A dynamic
view of oxide catalysts “at work” in oxidation processes</SPAN></B></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-US
style="FONT-SIZE: 14pt; FONT-FAMILY: Arial; mso-ansi-language: EN-US"><o:p></o:p></SPAN></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; LINE-HEIGHT: 17pt; TEXT-ALIGN: justify; mso-line-height-rule: exactly"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt; mso-bidi-font-family: 'Times New Roman'"><o:p> </o:p></SPAN></SPAN></P>
<P class=MsoBodyTextIndent
style="MARGIN: 0cm -7.2pt 6pt 0cm; LINE-HEIGHT: 17pt; TEXT-ALIGN: justify; mso-line-height-rule: exactly"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman">The objective of this report is to present a large family
of results aiming to: <B style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">first</I></B><I
style="mso-bidi-font-style: normal"> </I>illustrating the dynamic behavior of
oxide catalysts and of their surfaces in selective oxidation reactions, <B
style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">second</I></B>, showing the influence of
this behavior on the catalytic performances and <B
style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">third</I></B>, showing that improvements of
the performances of oxide catalysts can be obtained by orienting the dynamic
phenomena through well-thought-out
procedures.<o:p></o:p></FONT></SPAN></SPAN></P>
<P class=MsoBodyTextIndent
style="MARGIN: 0cm -7.2pt 6pt 0cm; LINE-HEIGHT: 17pt; TEXT-ALIGN: justify; mso-line-height-rule: exactly"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman">Many “symptoms” as i) modifications of crystalline
phases, oxidation states and crystals morphologies, ii) diffusion phenomena of
metals, reaction intermediates and spillover species, iii) evolutions of
catalytic performances with time-on-stream and iv) synergetic effects between
phases, point without ambiguity to the obsoleteness of “static view” of
catalysis, demonstrating the existence of dynamic phenomena at the surface of
catalysts “at work”. It is thus of an absolute priority to move towards a
“dynamic view” of catalysis, that considers “working catalysts” as quasi-living
objects and, in particular, takes into account the influence of the dynamic
processes that animate the catalytic surfaces “under its real state” on their
performances. Although being true for all kinds of catalysts and catalytic
processes, the dynamic approach is particularly relevant in the case of oxide
catalysts used in selective oxidation processes. Indeed, the mechanism of such
systems, namely the Mars & van Krevelen cycle, itself denotes dynamic
aspects. These are a continuous cyclic exchange of oxygen atoms between the gas
phase and the catalytic surface, and the occurrence of re-arrangements of
co-ordinations associated to the entrance and exit of oxygen into and from the
superficial structure of the oxides. In addition to give a “breathing aspect” to
working oxides, these phenomena intimately dictate their performances in
oxidation processes.<o:p></o:p></FONT></SPAN></SPAN></P>
<P class=MsoBodyTextIndent
style="MARGIN: 0cm -7.2pt 6pt 0cm; LINE-HEIGHT: 17pt; TEXT-ALIGN: justify; mso-line-height-rule: exactly"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman">We present results obtained from 3 reactions: 1) the
dehydration of 2-butanol to butenes in the presence of oxygen (DEHYD), 2) the
selective oxidation of isobutene to methacrolein (METH) and 3) the oxidative
dehydrogenation of propane to propene (ODP). The 3 reactions were carried out on
Mo-based oxide catalysts: MoO<SUB>3</SUB>, MoO<SUB>3-x</SUB>, MoO<SUB>2</SUB>,
Bi and Ni molybdates, eventually in physical contact with
Sb<SUB>2</SUB>O<SUB>4</SUB>. The samples were systematically characterized
before and after the catalytic reactions mainly by: XRD, XPS, confocal Raman
microscopy, SEM and AFM microscopy.<o:p></o:p></FONT></SPAN></SPAN></P>
<P class=MsoBodyTextIndent
style="MARGIN: 0cm -7.2pt 6pt 0cm; LINE-HEIGHT: 17pt; TEXT-ALIGN: justify; mso-line-height-rule: exactly"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman">The <B style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">1<SUP>st</SUP> CONCEPT</I></B> (using DEHYD)
aims at determining the environment of Mo atoms (i.e. the oxidation state or the
combination of oxidation states) stabilized under the conditions of reaction
leading to the highest catalytic performances. Crucial results are: 1)
MoO<SUB>3</SUB> used alone gets explosively reduced to MoO<SUB>2</SUB> during
the reaction, which corresponds to a deactivation, 2) the surface of
MoO<SUB>3</SUB> used in mixture with Sb<SUB>2</SUB>O<SUB>4</SUB> dynamically
stabilizes to a MoO<SUB>3-x</SUB> stoichiometry and exhibits high catalytic
performances, 3) Bi molybdates (</FONT></SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN
style="FONT-SIZE: 11pt; FONT-FAMILY: Symbol; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN
style="mso-char-type: symbol; mso-symbol-font-family: Symbol">a</SPAN></SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman">, </FONT></SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN
style="FONT-SIZE: 11pt; FONT-FAMILY: Symbol; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN
style="mso-char-type: symbol; mso-symbol-font-family: Symbol">b</SPAN></SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman"> and </FONT></SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN
style="FONT-SIZE: 11pt; FONT-FAMILY: Symbol; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN
style="mso-char-type: symbol; mso-symbol-font-family: Symbol">g</SPAN></SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman"> phases) used alone have superficial Mo atoms dynamically
stabilized during the reaction in a slightly reduced state and exhibit high
catalytic performances and 4° Bi molybdates used in mixture with
Sb<SUB>2</SUB>O<SUB>4</SUB> maintain superficial Mo atoms in a fully oxidized
state and suffer dramatic decreases of performances. These observations show
that: <B style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">the most performant environment of Mo in
oxide catalysts for the dehydration of 2-butanol is the slightly reduced
sub-oxidic MoO<SUB>3-x</SUB> one</I></B><I
style="mso-bidi-font-style: normal">.<o:p></o:p></I></FONT></SPAN></SPAN></P>
<P class=MsoBodyTextIndent
style="MARGIN: 0cm -7.2pt 6pt 0cm; LINE-HEIGHT: 17pt; TEXT-ALIGN: justify; mso-line-height-rule: exactly"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman">The <B style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">2<SUP>nd</SUP> CONCEPT</I></B> (using METH)
aims at understanding the origin of the highest performances in selective
oxidation processes of sub-oxidic MoO<SUB>3-x</SUB> state. Crucial results are:
5) the performances of Mo<SUB>8</SUB>O<SUB>23</SUB> sub-oxide used alone are
initially high but decrease with time-on-stream, 6) the performances of
Mo<SUB>8</SUB>O<SUB>23</SUB> used in mixture with Sb<SUB>2</SUB>O<SUB>4</SUB>
are lower than those of Mo<SUB>8</SUB>O<SUB>23</SUB> used alone but increase
with time-on-stream, 7) in both cases, shear structures of the sub-oxide
disappear under the working conditions, 8) MoO<SUB>3</SUB> used in mixture with
Sb<SUB>2</SUB>O<SUB>4</SUB> has its surface stabilized in a MoO<SUB>3-x</SUB>
stoichiometry (likely Mo<SUB>18</SUB>O<SUB>52</SUB>) and exhibits enhanced
performances compared to MoO<SUB>3</SUB> used alone, 9) in the presence of
Sb<SUB>2</SUB>O<SUB>4</SUB>, the surface of MoO<SUB>3</SUB> undergoes a dramatic
restructuring of the (010) faces of its crystals to (100) facets, which
corresponds to a real creation of active and selective catalytic sites. These
observations show that: <B style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">the high performances of MoO<SUB>3-x</SUB>
sub-oxide state are not due to shear structures but to the dynamic “breathing”
behavior of Mo atoms in the slightly reduced environment</I>.</B> This
environment is the only one bringing enough flexibility in the catalyst to
perform the Mars & van Krevelen cycles in a fast way, so explaining the best
performances observed in the case of the stabilization of sub-oxide material
during the reaction.<o:p></o:p></FONT></SPAN></SPAN></P>
<P class=MsoBodyTextIndent
style="MARGIN: 0cm -7.2pt 6pt 0cm; LINE-HEIGHT: 17pt; TEXT-ALIGN: justify; mso-line-height-rule: exactly"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt"><FONT
face="Times New Roman">The <B style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">two CONCEPTS</I></B> described above point
to two procedures offering the possibility to orient the dynamic behavior of
Mo-based oxides by modifying “in situ” the oxidation state of Mo atoms at work
to their most performing (selective) environment. The results reported above
point to a first procedure, namely <B
style="mso-bidi-font-weight: normal">the</B> <B
style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">addition in the catalysts formulation of an
external phase able to activate oxygen (</I></B>as </FONT></SPAN></SPAN><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN
style="FONT-SIZE: 11pt; FONT-FAMILY: Symbol; mso-bidi-font-size: 12.0pt">a</SPAN></SPAN><FONT
face="Times New Roman"><SPAN style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-SIZE: 11pt; mso-ansi-language: EN-GB; mso-bidi-font-size: 12.0pt">-Sb<SUB>2</SUB>O<SUB>4</SUB>,
BiPO<SUB>4</SUB>, SnO<SUB>2</SUB> etc.) A second procedure, very novel, is
described in the ODP on Ni molybdate. It is the injection of gaseous dopes (ppm
or some %) in the reaction gas during the reaction. It is shown that 10) the
injection of CO<SUB>2</SUB> brings about a stabilization of Mo at a higher
oxidation state with a corresponding selectivity loss while, 11) the injection
of N<SUB>2</SUB>O brings about a stabilization of Mo in a lower oxidation state
so promoting selectivity. CO<SUB>2</SUB> promotes a higher oxidation state of Mo
via the formation of monoatomic oxygen species (O<SUB>a</SUB>) resulting from
the dissociation of CO<SUB>2</SUB> on the catalyst (O<SUB>a</SUB> is more
oxidant than O<SUB>2</SUB>). N<SUB>2</SUB>O inhibits the adsorption of
O<SUB>2</SUB>, so limiting the formation of non-selective oxygen species (from
O<SUB>2</SUB>) and/or the oxidation rate of the catalysts. These observations
leads to a second procedure, namely <B style="mso-bidi-font-weight: normal"><I
style="mso-bidi-font-style: normal">adjusting the concentration of gas dopes in
order to modulate the selectivity by orienting the dynamic behavior of the
catalysts.</I></B></SPAN></SPAN><SPAN style="mso-bookmark: OLE_LINK2"><SUB><SPAN
lang=EN-GB
style="mso-ansi-language: EN-GB"><o:p></o:p></SPAN></SUB></SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: justify; mso-layout-grid-align: none"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-FAMILY: Arial; mso-ansi-language: EN-GB; mso-fareast-font-family: Batang; mso-fareast-language: KO"><o:p><FONT
size=3> </FONT></o:p></SPAN></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 14.2pt; TEXT-ALIGN: justify; mso-layout-grid-align: none"><SPAN
style="mso-bookmark: OLE_LINK2"><SPAN lang=EN-GB
style="FONT-FAMILY: Arial; mso-ansi-language: EN-GB; mso-fareast-font-family: Batang; mso-fareast-language: KO"><o:p><FONT
size=3> </FONT></o:p></SPAN></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm -4.05pt 0pt 0cm; TEXT-ALIGN: center"
align=center><SPAN style="mso-bookmark: OLE_LINK2"><SPAN
style="FONT-FAMILY: 'ITC Zapf Dingbats'; mso-bidi-font-family: Arial"><FONT
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