Trends in catalysis research

195 Pages·2006·26.173 MB·English

by  Lawrence P Bevy

CONTENTS
..
Preface
.tll
Chapter I Application of Plasma-Catalyst Hybrid Processes for
the Control ofNOx and Volatile Organic Compounds I
Hyun-Ha Kim. Atsuslti Ogata and Shigem Futamura
Chapter 2 Hydrotalcites as Potential Catalysts for Hydroxylation of Phenol
S Kannan
Chapter 3 Cluster Model Approach in Catalysis Research
A nihal Sien·aa/ra
Chapter 4 Recent Inquiries into the Mechanisms of Mctai-Salen
Catalyzed Asymmetric Oxidations ill
Konstantin P. Bn,liakov and Evgenii P. Talsi
Chapter 5 Utilization of Methane in the Catalytic Methylation of
Aromatics and Coal Liquefaction over Zeolite Catalysts
.Moses 0. Adehajo and Rm' L. Frost
Chapter 6 Transient Reaction Analysis of an Automotive
Catalyst on a Millisecond Time Scale
Yoshiyuki Sakamoto. Tomoyoshi Motohiro,
Kohei Okumura, Yoshimi Kizaki and Hirofiuni Shinjoh
Index ill
TRENDS IN CATALYSIS RESEARCH
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T h1•
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M 11enal hron1cmy prawem autorskun
PREFACE
The chemical or biological process whereby the presence of an external compound, a
catalyst, serves as an agent to cause a chemical reaction to occur or to improve reaction
performance without altering the external compound. CataJysis is a very irnponant process
from an industrial point of view since the production of most industrially imponant chemicals
involve catalysis. Research into catalysis is a major field in applied science, and involves
many fields of chemistry and physics. The new book brings together leading research in this
vibrant field.
Nonthemlal plasma (NTP) is gathering anentions as a powerful tool to induce various
chemical reactions at atmospheric pressure and room temperature. The application fields of
NTP processing include air pollution control, sterilization, surface modification, optical
application. instrumental analysis, water treatment, ozone generation, fuel refom1ing and so
fonh. Despite the long history of electrical corona discharge, its application to air pollution is
relatively a new field. Chapter I describes the historical development and up-to-date
evaluation of the NTP technology for the removal of NOx and volatile organic compounds
(VOCs). Especially, this chapter focused on the culling-edge technology of hybrid NTP
process, which combines NTP with various types of catalysts to improve energy efficiency
and the reaction selectivity. Historical landmark in the development of NTP technology and
current state-of-an technology of plasma-catalyst hybrid processes for the removal of NOx
and VOCs arc discussed.
Hydrotalcites are two dimensional layered materials. are receiving increased auention in
recent years for their diverse applications like catalysts, supports, ion-exchangers, additives
and precursors for multi-component catalysts. StructuraJiy. these materials can be perceived
2
by starting with brucite (Mg(OHh) structure wherein, a partial substitution of Mg by a
'
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trivalent metal ion, say Al occurs and the resulting excess positive charge of the sheets are
+,
compensated by anions, which occupy the interlayer positions along with water molecules.
The genera.! formula of these materials can be represented as [M(IT) .,M(Ill)x(OH)2] [A •·
1
llln].mHzO where M(H), M(JII) and A arc bivaJcnt metal ion, trivalent metaJ ion and interlayer
anion and 'x' can usually have values around 0.2-0.4. The wide maneuverability of these
layered materials by incorporating a gamut of varied metal ions and incorporation of any
anions irrespective of their size and charge gives enonnous scope for tailoring these materials
for specific applications. 1n chapter 2, an overall view of these materials including their
synthesis and characterization and subsequently how these materia.ls are exploited for
'vtatenal chron1ony prawefll autorskun
Lawrence I'. Bevy
VIII
selective hydroxylation of phenol, one of the industrially important reactions, to
dihydroxybenzenes wiU be given. This chapter encompasses background of these materials,
synthesis of specific materials, characteri.zation of them and their catalytic behavior. An
attempt also will be made wherever possible for Slructure-activity relations. A travel wherein
the catalytic behavior will be journeyed through different classes of hydrotalcites namely
binary and ternary hydrotalcites with specific metal ions (bivalent, trivalent and tetravalent
metal ions) in brucite-like sheets and analyz·ing 1he merits and demerits of them to derive
broader conclusions. In this journey, influence of synthesis methodology wiiJ also be
traversed to bring out its importance. A future scope of utilizing these materials for such
cataly1ic seleclive oxida1ion reactions will be summarized.
Chapter 3 presents a brief guide on the applica1ion of the cluster model approach to the
invcsligation in the catalytical area. First, it describes the underlying theory, followed by the
discussion of some recent examples. Since the clus1er model approach is founded on the
existence of local phenomena, section 2 presents an introdu.ction on this important concept. In
order 10 describe local phenomena, different calcula1ion strategies may be employed. Section
3 briefly describes the most common among these slratcgics. Finally, section 4 presents some
examples on hydrodcsulphurizalion (HDS), supported/exchanged zeolite catalysts and other
intcres1ing catalytic systems. This chapter does no intend to be an exhaustive review of the
field of the cluster model approach. It is a introductory vison about the use of ab initio
calculations, in the area of the cluster model approaches to model catalytic phenomena, and
includes successes as well as failures and/or drawbacks of these methods.
Since 1990s, metal-salen catalyzed asymmetric oxidations became very popular, so that
Ill .
the Jacobsen's Mn (salen)CI complex was named Fluka Reagent of the year 1994. The
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Katsuki-Jacobsen Mn (salen)CI catalyzed cpoxidation of unfunctionalized olefms probably
attracted the greatest attention among the chiral metal-salen catalytic systems. Any
information on the intermediates could be of practical value for deeper understanding of the
catalytic action of the system as well as could contribute to fundamental knowledge on
oxidation reactions. In chapter 4, the authors present recent mechanistic studies of
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[Mn (salen)CI] catalyzed oxidations of unfunctionalized olefins. It was shown that different
intermediates operate in these systems depending on the terntinal oxidant used:
manganese(lll) acylperoxo complex [Mn111(salen){00C0Aryl)] with m-chloroperoxybenzoic
2
acid (m-CPBA) and d low-spin oxomanganese(V) complex [Mn vO(salen)L] with
iodosobcnzcnc (PhlO). Also, an anti ferromagnetically coupled binuclear manganese
J.I·OXO
1
1 cr
(IV) species of the type [(salen)LMn vOMnv(salen)L ') (L, L'= or PhlO) acting as a
reservoir of the active species were detected. These results are compared with those obtained
for [Crm(salcn)CI] catalyzed asymmetric oxidations of olefins by PhiO. The active
intermediate of these systems was detected and identified as [CrvO(salen)L] (where L= Cl- or
a solvent molecule). A reservoir of the active species in this system was also found to exist as
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a mixed-valence binuclear species [L(salen)Cr 0Crv(salen)L') (L, L'= Cr or solvent
molecules). The high-valence Cr complexes are in equilibrium and their ratio can be affected
by addition of donor ligands (DMSO, DMF, H 0). The third class of systems to be discussed
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here appeared in the last years, reflecting the growing need in simple and non-toxic systems
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for suliide oxidation. Chinll [Fe (salen)CI] complexes were synthesized and used as catalysts
for asymmetric oxidation of several alkylar:yl sulfides with PhJO. Surprisingly, the reactive
intermediate in this system was found different from those detected in Mn-salen and Cr-salen
Mate11al chroniony prawem autorsk1m
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Pre lace
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based catalytic systems. Namely, the intermediate was shown to be an iodosylbenzene
iron(lll)(salcn) complex similar to iodosylbenzene-iron(lll) porphyrin intermediates recently
discussed in the literature. The data obtained are analyzed to understand some catalytic
properties of these systems.
The present world reserves of natural gas that contain mainly methane are still
underutilized due to high cost of transportation. Considerable interest is therefore presently
shown in the conversion of methane to transportable liquids and feedstocks in addition to its
previous sole use for heating purposes by combustion. One possible new route for the
utilization of methane de.rived from natural gas or other sources for conversion to more
valuable higher hydrocarbons is the methylation of aromatic hydrocarbons. Chapter 5
provides a general overview of the work that has been done so far on the use of methane for
catalytic methylation of model aromatic compounds and for direct liquefaction of coal for the
production of liquid hydrocarbons. The chapter is especially focused on the use of both acidic
and basic zeolites in acid-catalyzed and base-catalyzed methylation reactions. respectively.
The base-catalyzed methylation reaction covered in this discussion is mainly the oxidative
methylation of toluene to produce ethylbenzenc and styrene. This reaction has been found to
occur over basic sites incorporated into zeolites by chemical modification or by changing the
electronegative charge of the zeolite framework.
There are two key points to develop an excellent purification system for automotive
exhaust gas. The first one is to analyze the transient reactions of the catalyst_ because the
components of automotive exhaust gas are not stable during the engine operation and an
aggrcssi\le- usage of the transient reactions is considered to be one of the items to overcome
strict regulations of automotive exhaust gas. The second is to design the catalyst synthesized
by e.ach of nano materials. Chapter 6 studies an automotive catalyst from the above points, lhe
have developed a new apparatus: time-resolved time-of-flight mass spectrometry with
author~
molecular-pulse-probes for analysis of dynamic processes in surface catalytic reactions on a
millisecond scale (TMPRAS; TM+). The method using TM+ enable us analyze a transient
reaction of a catalyst under the high-pressure condition. which is simulated actual automotive
exhaust gas on a millisecond time scale. It is possible for TM+ to measure catalysis reactions
both of an actual usage catalyst and of a model catalyst. This method can bridge the gap
between surface science and an actual catalyst, what can be called pressure gap and material
gap. Firstly, TM+ is described from the viewpoints of the vacuum system and signal
processing. Secondly, some examples arc shown as follows; CO oxidation on a platinum lilm.
an oxygen storage reaction on a slurry-coated catalyst. oxygen isotopic exchange reaction on
a Pt/ A 10 pellet sample and NO decomposition on a precious metal electrode.
1 3
'vtatenal chron1ony prawefll autorskun
In: 'J rends ln Catalysts Research lSHN 1-59454-659-2
Editor: Lawrence P. Bevy, pp. 1-50 © 2006 Nova Science Publishers, Inc.
Chapter 1
APPLICATION OF PLASMA-CATALYST HYBRID
PROCESSES FOR THE CONTROL OF NOX AND
VOLATILE ORGANIC COMPOUNDS
Hyun-Ha Kim', Atsushi Ogata and Shigeru Futamura
National Institute of Advanced Industrial Science and Technology (AIST)
AIST Tsukuba West, 16-1 Onogawa, Tsukuba, lbaraki 305-8569, Japan
ABSTRACT
Nonthennal plasma (NTP) is gathering attentions as a powerful tool to induce various
chemical reactions at atmospheric pressure and room temperature. The application fields
of NTP processing include air pollution control. sterilization, surface modification,
optical application, instrumental analysis, water treatment, ozone generation, fuel
reforming and so forth. Despite the long history of electrical corona discharge, its
application to air pollution is relatively new field. This chapter describes the historical
development and up-to-date evaluation of the NTP technology for the removal of NOx
and volatile organic compounds (VOCs). Especially, this chapter focused on the cutting
edge technology of hybrid NTP process, which combines NTP with various types of
catalysts to improve energy efficiency and the reaction selectivity. Historical landmark in
the development of NTP technology and currcm state-of-an technology of plasma
catalyst hybrid processes for the removal of NO.r and VOCs are discussed.
Keywords: nonthermal plasma (NTP); catalyst; dielectric-barrier discharge; plasma-driven
catalysis; pulsed corona discharge; air pollution; VOCs; NOx
I.
INTRODUCTION
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There are a number of problems facing mankind today such as ever-mcreasmg
population, global warming, rapid urbanization/industrialization many developing
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E-mail: [email protected] Tel: [phone]
Maknal chromony prawel" autorskrm
2 Hyun-Ha Kim, AtSushi Ogata and Shigeru Futamura
countries, ozone layer depletion in the stratosphere, climate changes and desertification etc. In
more recent rimes, concern about the atmospheric pollution has widened to include damages
to buildings and materials, forestS, agricultural products and even the stratosphere. Especially
recent pollution problems are not confined to regional ones any more because of the long
distance transportation over the border. The need for bener quality is also emphasized for the
indoor air since most people spend more than 90% of times indoor environment. The public's
concern about the qualiry of environment keeps increasing every year. The emission
regulations for the hazardous chemical compounds all the more stringent in many
b~ome
countries. There are two major approaches for the pollution prevention. One is the source
reduction and the other one is end-of-pipe treauncnt. Although the source reduction is an
environmental friendly solution for the control of pollutant emission. this approach alone
cannot meet the regulaLion in most cases. It is therefore necessary to develop cost-efficient
end-of-pipe treatment with high performance.
Among the various air pollution control techniques, two important technologies discussed
in this chapter are nonthermal plasma (NTP) and catalyst. Catalyst technology has been used
in many industrial fields such as oil chemistry, pollution control, chemical synthesis, etc.
Environmental application of catalytic technology has been started in the 1970s mostly for the
cleaning of exhaust gas from cars. The catalyst technology used in the environmental
protection field is also referred to as environmental catalytic process. Three-way catalyst
(TWC), for exan1ple Pt-Rh-Ce0 , is one of representative environmental catalysts. The
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progress of industry requires further enhancement of catalytic perfonnance. One example is
the need for new catalyst capable of controlling NO.r emission from lean-bum engine. The
application of NTP to environmental problems and to green chemistry is emerging fields that
offer unique opportunities for advancement. The history of NTP to the environmental
protection has more than I 00 years experience, mostly for the ozone generation in the water
treatment facilities. Early studies on the NTP application for air pollution control started in
1970s, and gathered a considerable attention in the 1980s. Through the extensive research and
development (R&D) effortS by many research groups in many countries, significant progress
has been made during the last two decades. There also have been some review articles and
books both on the fundamental, historical development and on the engineering of
asp~tS
NTP [ 1-8].
The purpose of this chapter is to provide the historical development and the recent R&D
activities of the atmospheric-pressure nonthermal plasmas as an end-of-pipe treatment
technology for the abatement of hazardous air pollutants. The major gas-phase air pollutants
dealing with in this chapter include NOx, volatile organic compounds (VOCs), and particulate
mauers (PMs) from diesel engine. Especially, this chapter deals with the combined system of
NTP and catalyst, which takes advantage of a synergy of both technologies. The rype of the
hybrid systems varies quite wide range depending on the configuration, types of catalyst and
plasmas. The classification of combination, basic structure, the working principle of the each
system, historical development of NTP, current achievement and future prospects will be
presented.
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Application of Plasma-Catalyst Hybnd Processes for the Control of NOx . . . 3
2.
ENVIRONMENTAL PROBLEMS RELATED TO NOX AND VOCS
2.1. Photochemical Smog
Two well-known air poiJutants of NOx and VOCs are highly correlated each other in
terms of photochemical smog. As one can see from the LA smog accident, this photochemical
smog mostly occurs in urban areas. Three key factors in the formation of photochemical smog
arc NOx, YOCs and the presence of suo light (mostly UV). Photochemical reactions between
NOx-VOCs produce peroxyacyl nitrates (PANs), ozone, aldehydes and so on. which arc
highly irritating chemicals. PANs arc now recognized to be ubiquitous in polluted urban
atmosphere [9]. Ozone was found to be a major component of photochemical smog.
YOCs arc emiued mostly from the industrial activity such as the use of solvent,
petroleum industry, combustion etc. Most of YOCs arc known to as carcinogen or suspected
carcinogen. Definition of YOCs differs from countries. For example, U.S.A clean air act
defines YOCs as "a chemical compounds that can be a precursor of photochemical smog".
EU defmes YOCs based on its vapor pressure (larger than 0.0 I kPa at 293.15K). However,
the main purpose of YOCs emission regulations is to reduce photochemical smog by
controlling the emission of VOCs. The technical term of "photochemical smog" was coined
by the early works of Haagen-Smit in 1950s to find the reason of eye irritation complaint in
Los Angeles area [I OJ. They found that the maio eye irritating chemical was ozone. Later on
studies revealed the presence ofN0 and peroxyacetyl nitrate (PAN) together with ozone.
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Anthropogenic emission sources of NOx are mostly related to the combustion processes
such as industrial boiler. car engine. coal-oil fired power plant etc. Jn the flue gases from
combustion process including engine, NOx is mostly emitted as NO(> 95%). Car engines arc
the main source of NOx in urban area. which is highly related to the photochemical smog
problem.
The overall mechanism of photochemical smog formation together with their line in the
atmosphere is illustrated in Figure I. Generally speaking, photochemical smog is a result of
consecutive chain reactions involving atoms and free radicals. Chain initiation step in the
photochemical smog is the photolysis of molecules (N0 0 aldehydes etc.), resulting in the
2, 3,
formation of free radicals. NOx is initially emitted into the atmosphere as NO, and then
slowly converted to N0 via R I. In daytime the produced undergoes photolysis, R2. to
2 N~
form NO and ground state atomic oxygen, oeP) . The photolysis ofN02 has a quantum yield
of unity at wavelengths below 370 nm.
(R I)
N02 + hv (!.< 420om)-+ 2NO + oeP) (R2)
(R3)
(R4)
'vtatenal chron1ony prawefll autorskun
4 Hyun-Ha KJm, Atsushi Ogata and Sh1geru Futamura
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-'o~
/ I '
Photochemical oxidants
RCO
RCHO
OH
.-· RC(0)0
2
I
RO
NO RC(O)O RO,
R
t----. -
OH
/ VOCs
VOCs
NO
Acid rain
00 00 00
co 00 00
Figure I. Photochemical smog fom1ation in the atmosphere (R: alkyl radical, RO: alkoxy radicaL RCO:
acyl radical. R0 2: Pcroxyalkyl radical. RCOO~: Acylperoxyl radical)
The atomic oxygen recombines with oxygen molecule to form ozone. In lhe absence of
VOCs, produced ozone reacts with NO and a steady-state is achieved in which the ozone
concentration is given as follows.
( I )
This successive reactions of R2- R3 called as a shon-term NOx-cycle, and there is no
significant 0 3 build-up. When lhe VOCs are present in the atmosphere, however. various
radicals of hydrocarbons are produced. The OH radical-hydrocarbon reaction plays dominant
role in most cases, and ozone and N0 radical for olefins chemistry. Especially. oxidative
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decomposition of VOCs produce some peroxy radicals of peroxyalkyl radical (R0
2),
acylperoxy (RC(0)0 radical and hydorperoxyl radical (H0 which are the chain carriers i.n
) ),
2 2
lhe conversion of NO to N0 This process involving peroxy radicals provides new palhway
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for the conversion of NO to NOz not involving OJ and resulting in the accumulation of ozone.
(RS)
NO + RO, -+ N0 + R0,,. (R6)
2 1
These NO oxidation processes by peroxy radicals play very imponant role in the NOx
removal using the NTPs. Formation of PAN is also one of chain termination reaction between
peroxyacetyl radical (RC(O)Oz) radical and NOz.
Maknal chromony prawe!" autorsk1r1