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Mesoporous and microporous materials: Recent advances
N14
June 1995, p. 51. Simon, a business professor at the University of Maryland has challenged others to name ‘any trend pertaining to human welfare’ and to place a wager as to whether that trend would get worse over time. Two scientists have responded, but as yet it has not been agreed as to whether the trends suggested will be acceptable for the wager. The two scientists, when told that these topics might not be acceptable to Simon, responded that he could take it or leave it, adding ‘Frankly, astronomers don’t spend their time debating with flat-earthers, and evolutionists don’t spend their time debating with creationists.’ This displays the root of the problem, since it is precisely these types of debate that are needed if our science is to move forward. So although the answer to the title question is that catalysis is difficult, we must persevere and get it right. It is too important to society for us to fail. What is required is the correct focusing of our efforts and fundings, if we aim to succeed. We need new catalysts and processes and, although these will come by detailed stepwise increments in our knowledge base, we also need the massive step changes in technologies. In the UK, the Technology Foresight review identified low-temperature CH4 oxidation as a key goal. A number of us have known this for a long time and have tried, but, apart from the many publications, there has not yet been much to show. However, nature got there millions of years ago, since the room temperature activation of CHI is an everyday occurrence for methylmonooxygenese. Nature shows us that we have a lot to learn, but nature also gives us a clue - it can be done. The knowledge that a target is achievable is a big help. Of course we have
applied catalysis A: General
had help from thermodynamics for many years now that can tell us when a specific target is impossible, e.g. perpetual motion. This could have helped some people who were caught up in a wager on this topic at the beginning of the nineteenth century, since lack of knowledge can be very costly: “Mr. Gobert of Philadelphia,
who lately
advertised that he would take any bet from five to one hundred thousand dollar on the feasibility
of Mr. Redheffer’s
perpetual
motion,
discovery
of
was taken up for five
thousand dollars, by Mr. Jacob Perkins of Newburyport. periments
After making a series of ex-
in vain, to construct
a moving
machine upon Mr. Redheffer’s self moving principle,
he discovered to his infinite cha-
grin, that Mr. Redheffer had in the meantime moved himself off, with 20,000 dollars in notes of hand given him by Mr. Gobert for his valuable secret. We understand that Mr. Gobert has acknowledged
his bet for-
feited, and is now in pursuit of Redheffer, who keeps himself in perpetual
motion to
elude him. I1(Weekly Register, 1813)
GRAHAM HUTCHINGS
Mesoporous and Microporous Materials: Recent Advances
Zeolite p has recently become a fashionable zeolite for study. For a long time zeolite ,!?was eclipsed by the subsequent development of the zeolite ZSM-5 as the wonder catalyst of the 1970’s and 1980’s, but zeolitefi is now finding potential uses in a number of processes. Pan of the interest lies in the structure of zeolite p since one of the polymorphs can potentially exist in a chiral form. Recently, Paul Volume 129 No. 2 - 31 August 1995
N15
Cox at Portsmouth, UK has postulated a mechanism for faulting in zeolite b [A.P. Stevens and Paul A. Cox, J. Chem. Sot., Chem. Commun., (1995) 3431. They have used molecular modelling, based on the Biosym software, to predict the locations and orientations adopted by the 1,l-dibenzyl-1 ,l -dimethylammonium template cations to the zeolite. They have then used this to rationalise the vast array of data available for zeolite B concerning crystallographic faulting. Another material that has received considerable attention is structured mesoporous MCM41. One problem associated with this material is that, unlike zeolites, the long range order of the mesoporous structure is not usually significant. An attempt has been made to overcome this problem by Ryoo and Kim [J. Chem. Sot., Chem. Commun., (1995) 7111, who have used powder X-ray diffraction, “Si and “‘Xe NMR spectroscopy to study this problem. They have shown that long range structural order and textured uniformity can be significantly improved when acetic acid is added repeatedly during the preparation. The authors attribute the effect to a shift in the reaction equilibrium of the crystallisation process. A novel use of MCM41 as a catalyst for acid and base catalyzed reactions is described by Kloestra and Van Bekkum [J. Chem. Sot., Chem. Commun., (1995) 10051.They have used the caesium and sodium form of MCM-41 and have shown that these are selective, water stable and recyclable catalysts for the base-catalyzed Knoevanagel condensation and the acidcatalyzed acetalisation and alcohol condensation. However, MCM-41, when impregnated with caesium acetate, was shown to act as a base catalyst for the
applied catalysis A: General
Michael addition reaction. This demonstration of reaction flexibility indicates that MCM41 will have as extensive reaction chemistry as its microporous analogues and this should promote further research in this interesting area. One major development, awaited for some time by many, has now been announced. This involves the enhancement in activity of VPI-5 for acid catalyzed reaction. Groups in Spain [S. del Val, J. Blasco, E. Sastre and J. Perez-Pariente, J. Chem. Sot., Chem. Commun., (1995) 7311 have found a novel method to introduce Si into VPI-5 and have synthesised the siliconsubstituted material. They have shown its use for the acid catalyzed m-xylene isomerisation and disproportionation reactions However, the substitution does not appear to have improved the chemical stability of this material since it still is prone to structure collapse on heating. GRAHAM J. HUTCHINGS
Water-gas Shift Reaction Studies: A Further Exploration of Controversy?
Water-gas shift reaction chemistry has been well studied and the author has recently reviewed a large amount of the experimental evidence for this reaction [see Rhodes et al., Catal. Today, 23 (1995) 431. Two recent papers are quite thought provoking. Work reported from the group of Campbell [J. Yoshirhara, S.C. Parker, A. Schafer and C.T. Campbell, Catal. Lett., 31 (1995) 3131 concerns both the reverse water-gas shift reaction and the related methanol synthesis over clean polycrystalline copper. They report a detailed kinetics study for the simultaneous reactions and report an abVolume 129 No. 2 - 31 August 1995
June 1995, p. 51. Simon, a business professor at the University of Maryland has challenged others to name ‘any trend pertaining to human welfare’ and to place a wager as to whether that trend would get worse over time. Two scientists have responded, but as yet it has not been agreed as to whether the trends suggested will be acceptable for the wager. The two scientists, when told that these topics might not be acceptable to Simon, responded that he could take it or leave it, adding ‘Frankly, astronomers don’t spend their time debating with flat-earthers, and evolutionists don’t spend their time debating with creationists.’ This displays the root of the problem, since it is precisely these types of debate that are needed if our science is to move forward. So although the answer to the title question is that catalysis is difficult, we must persevere and get it right. It is too important to society for us to fail. What is required is the correct focusing of our efforts and fundings, if we aim to succeed. We need new catalysts and processes and, although these will come by detailed stepwise increments in our knowledge base, we also need the massive step changes in technologies. In the UK, the Technology Foresight review identified low-temperature CH4 oxidation as a key goal. A number of us have known this for a long time and have tried, but, apart from the many publications, there has not yet been much to show. However, nature got there millions of years ago, since the room temperature activation of CHI is an everyday occurrence for methylmonooxygenese. Nature shows us that we have a lot to learn, but nature also gives us a clue - it can be done. The knowledge that a target is achievable is a big help. Of course we have
applied catalysis A: General
had help from thermodynamics for many years now that can tell us when a specific target is impossible, e.g. perpetual motion. This could have helped some people who were caught up in a wager on this topic at the beginning of the nineteenth century, since lack of knowledge can be very costly: “Mr. Gobert of Philadelphia,
who lately
advertised that he would take any bet from five to one hundred thousand dollar on the feasibility
of Mr. Redheffer’s
perpetual
motion,
discovery
of
was taken up for five
thousand dollars, by Mr. Jacob Perkins of Newburyport. periments
After making a series of ex-
in vain, to construct
a moving
machine upon Mr. Redheffer’s self moving principle,
he discovered to his infinite cha-
grin, that Mr. Redheffer had in the meantime moved himself off, with 20,000 dollars in notes of hand given him by Mr. Gobert for his valuable secret. We understand that Mr. Gobert has acknowledged
his bet for-
feited, and is now in pursuit of Redheffer, who keeps himself in perpetual
motion to
elude him. I1(Weekly Register, 1813)
GRAHAM HUTCHINGS
Mesoporous and Microporous Materials: Recent Advances
Zeolite p has recently become a fashionable zeolite for study. For a long time zeolite ,!?was eclipsed by the subsequent development of the zeolite ZSM-5 as the wonder catalyst of the 1970’s and 1980’s, but zeolitefi is now finding potential uses in a number of processes. Pan of the interest lies in the structure of zeolite p since one of the polymorphs can potentially exist in a chiral form. Recently, Paul Volume 129 No. 2 - 31 August 1995
N15
Cox at Portsmouth, UK has postulated a mechanism for faulting in zeolite b [A.P. Stevens and Paul A. Cox, J. Chem. Sot., Chem. Commun., (1995) 3431. They have used molecular modelling, based on the Biosym software, to predict the locations and orientations adopted by the 1,l-dibenzyl-1 ,l -dimethylammonium template cations to the zeolite. They have then used this to rationalise the vast array of data available for zeolite B concerning crystallographic faulting. Another material that has received considerable attention is structured mesoporous MCM41. One problem associated with this material is that, unlike zeolites, the long range order of the mesoporous structure is not usually significant. An attempt has been made to overcome this problem by Ryoo and Kim [J. Chem. Sot., Chem. Commun., (1995) 7111, who have used powder X-ray diffraction, “Si and “‘Xe NMR spectroscopy to study this problem. They have shown that long range structural order and textured uniformity can be significantly improved when acetic acid is added repeatedly during the preparation. The authors attribute the effect to a shift in the reaction equilibrium of the crystallisation process. A novel use of MCM41 as a catalyst for acid and base catalyzed reactions is described by Kloestra and Van Bekkum [J. Chem. Sot., Chem. Commun., (1995) 10051.They have used the caesium and sodium form of MCM-41 and have shown that these are selective, water stable and recyclable catalysts for the base-catalyzed Knoevanagel condensation and the acidcatalyzed acetalisation and alcohol condensation. However, MCM-41, when impregnated with caesium acetate, was shown to act as a base catalyst for the
applied catalysis A: General
Michael addition reaction. This demonstration of reaction flexibility indicates that MCM41 will have as extensive reaction chemistry as its microporous analogues and this should promote further research in this interesting area. One major development, awaited for some time by many, has now been announced. This involves the enhancement in activity of VPI-5 for acid catalyzed reaction. Groups in Spain [S. del Val, J. Blasco, E. Sastre and J. Perez-Pariente, J. Chem. Sot., Chem. Commun., (1995) 7311 have found a novel method to introduce Si into VPI-5 and have synthesised the siliconsubstituted material. They have shown its use for the acid catalyzed m-xylene isomerisation and disproportionation reactions However, the substitution does not appear to have improved the chemical stability of this material since it still is prone to structure collapse on heating. GRAHAM J. HUTCHINGS
Water-gas Shift Reaction Studies: A Further Exploration of Controversy?
Water-gas shift reaction chemistry has been well studied and the author has recently reviewed a large amount of the experimental evidence for this reaction [see Rhodes et al., Catal. Today, 23 (1995) 431. Two recent papers are quite thought provoking. Work reported from the group of Campbell [J. Yoshirhara, S.C. Parker, A. Schafer and C.T. Campbell, Catal. Lett., 31 (1995) 3131 concerns both the reverse water-gas shift reaction and the related methanol synthesis over clean polycrystalline copper. They report a detailed kinetics study for the simultaneous reactions and report an abVolume 129 No. 2 - 31 August 1995