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<DIV align=center><FONT face=Arial size=2><A name=OLE_LINK2><STRONG><SPAN
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size=3>Seminarios del Dpto. de Química Inorgánica, Analítica y Química Física /
INQUIMAE</FONT></SPAN></STRONG></A><SPAN style="mso-bookmark: OLE_LINK2"><SPAN
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Universidad de Buenos Aires</SPAN></STRONG></SPAN><SPAN
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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
<FONT color=#ff00ff>20</FONT> 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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style="COLOR: black; FONT-FAMILY: Arial; mso-ansi-language: ES-AR">Ciudad
Universitaria, Pab. II, Piso 3</SPAN></STRONG></SPAN><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>
<P class=MsoNormal
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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
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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
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size=3>iiiii</FONT></SPAN></SPAN><SPAN
style="FONT-FAMILY: 'ITC Zapf Dingbats'; mso-bidi-font-family: Arial"><o:p></o:p></SPAN></P></FONT>
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<P></P>No virus found in this incoming message.<BR>Checked by AVG Free
Edition.<BR>Version: 7.1.409 / Virus Database: 268.14.6/535 - Release Date:
15-Nov-06<BR></BLOCKQUOTE>
<P>
<HR>
<P></P>No virus found in this incoming message.<BR>Checked by AVG Free
Edition.<BR>Version: 7.1.409 / Virus Database: 268.14.6/535 - Release Date:
15/11/2006<BR></BODY></HTML>