Shin-ichi Nakata

Cerium impregnated H-mordenite as a catalyst for shape-selective isopropylation of naphthalene. Selective deactivation of acid sites on the external surface

Abstract The impregnation of cerium is the effective method for the deactivation of external acid sites of H-mordenite. The selectivity of 2,6-DIPN in the isopropylation of naphthalene was enhanced by the impregnation with such a large amount as 30–50 wt.-% of cerium without significant decrease of catalytic activity. The highest selectivity of 2,6-DIPN was achieved up to 70% over a highly dealuminated H-mordenite, (HM(128); SiO 2 /Al 2 O 3 = 128, with 30 wt.-% of cerium. The enhancement of the selectivity is ascribed to the deactivation of external acid sites judging from the activity of the cracking reaction of 1,3,5-triisopropylbenzene. The effective pore radius was not reduced by the modification. The ceria is highly dispersed only on the external surface of H-mordenite without any formation of new kinds of acid sites. The 129 Xe NMR observation suggfests that cerium is not in the pores, but on the external surfaces. The deactivation of the external acid sites is a characteristic property for cerium. Lanthanum and neodymium inhibited catalytic activity of the isopropylation because the pores were narrowed by their impregnation. A possible reason of the deactivation is ascribed to the amphoteric property of ceria.

Investigation of the factors influencing the structural stability of mesoporous silica molecular sieves

Abstract Structural stability of mesoporous molecular sieves synthesized under various conditions were investigated. The effect of synthesis temperature, compositions, and silica source was examined. The MCM-41 synthesized from fumed silica and FSM-16 synthesized from kanemite was the most stable towards water, retaining the regularity for more than 90 days; the sample synthesized from TEOS at room temperature was less structurally stable. It is considered that the regularity loss involves the adsorption of water onto the surface silanol groups, which causes the nearby Si–O–Si bond cleavage, eventually resulting in the structural collapse. The X-ray powder diffraction, N 2 adsorption, and NMR study revealed that the structural stability has a strong correlation with the ratio of pore wall thickness t to the amount of SiOH, while such stability is weakly correlated with each parameter.

Mechanical Stability of Mesoporous Materials, MCM-48 and MCM-41

The structural collapse of mesoporous molecular sieves, MCM-48 and MCM-41 materials by mechanical compression was found to occur mechanochemically through hydrolysis of Si–O–Si bonds. Their ordered structures were retained by compressing the well-dried samples under dry N2. Trimethylsilylation of mesoporous materials proved effective in eliminating their instability to compression through enhancing hydrophobicity.

31P-MASNMR spectroscopic studies with zirconium phosphate catalysts

Zirconium phosphates are crystallized during the removal of hydration water in the zirconium phosphate gel with phosphoric acid solution under reduced pressure. Several forms of crystallites are obtained by this procedure, depending on the temperature and process time, for a given concentration of phosphoric acid. Synthetic ZrP2O7 and e-Zr(HPO4)2 catalysts, which were evacuated at 773 K, showed higher catalytic activities for butene isomerization than other forms of zirconium phosphates or other conventional solid acid catalysts. In order to elucidate those higher catalytic activities, 31P magic angle spinning NMR (31P-MASNMR) has been employed to study zirconium phosphates after evacuation at different temperatures. The 31P chemical shifts move towards higher magnetic fields as the layer separations become smaller. The catalysts which showed higher activities showed higher chemical shifts at around −38 ppm from H3PO4. These results suggest that the phosphate groups remaining after evacuation at around 800 K may enhance the protonic characteristics, since the accumulation of electrons moves from the phosphate groups on the surface to phosphorus atoms which are located between Zr atom planes.

Structure and surface chemistry of crystalline zirconium phosphate catalysts

Abstract The catalytic activities for isomerization of butenes and cyclopropane on crystalline zirconium phosphates(ZrP) have been examined. The ZrP catalyst, when calcined at higher temperatures( ca. 800K), exhibited higher catalytic activities. The coisomerization of d0- and ds-1-butene suggests that isomerization would proceed on protonic acid sites even after heat treatment at 1100K. After evacuation at ca. 800K, most of the phosphate groups were removed, with consequent loss of water, due to the condensation of phosphate groups between each Zr atom layer. However, a trace amount of residual phosphate groups still remained on the surface. In order to elucidate those higher catalytic activities on the phosphate protons, 31P magic angle spinning NMR (31P-MASNMR) has been employed to study the phosphorus micro-environments. The catalysts which showed higher activities showed higher 31P chemical shifts. The NMR results suggest that the phosphate groups remaining after evacuation at around 800 K may enhance the protonic acidity.

A new concept for catalysts of asphaltene conversion

Abstract One must understand the mechanism of bottoms cracking in asphaltene conversion in order to design a catalyst to affect this change. Asphaltene molecules are big, multiple stacked, porphyrin structures containing high concentrations of heteroatoms. They readily deactivate catalysts. Until now, the first stage of asphaltene conversion has not been given much attention. This first stage, that of demetallization, has been regarded as a simple metal take-up zone which guards the subsequent hydrotreating portion of the catalyst from undue fouling by metal sulfides. Large pore size and good strength are more important for a demetallization catalyst than are hydrotreating activity. Supported sepiolite catalysts and modifications thereof are good candidates to meet these targets.

133Cs and 23Na MAS NMR studies of zeolite X containing cesium

Abstract The local structures around cesium and sodium in the zeolites X containing cesium in excess of the ion-exchange capacity (cesium-added zeolite X ) were examined by 133Cs and 23Na MAS NMR to elucidate the location of the added cesium and the formation of the basic sites caused by addition of the excess cesium. The cesium species located in the intracrystalline cavities of zeolite and those on the outer surface of zeolite crystallites were distinguished by a combination of 133Cs and 23Na MAS NMR data. The excess cesium species are located in the supercages for the samples containing an excess of 1.1 and 2.9 cesium atoms per supercage, whereas for the samples containing 5.1 and 9.8 cesium atoms per supercage, parts of the cesium species are on the outer surface of the zeolite crystallites. The cesium-added zeolites which contain cesium species in the supercages and possess a high surface area exhibit high activities for 1-butene isomerization.

Selective synthesis of ethylenediamine from ethanolamine over modified H-mordenite catalyst

The synthesis of ethylenediamine (EDA) from ethanolamine (EA) with ammonia over acidic types of zeolite catalyst was investigated. Among the zeolites tested in this study, the protonic form of mordenite catalyst that was treated with EDTA (H-EDTA-MOR) showed the highest activity and selectivity for the formation of EA: at 603 K, W/F=200 g h mol −1 , and NH 3 /EA=50. The reaction proved to be highly selective for EA over H-EDTA-MOR, with small amounts of ethyleneimine (EI) and piperazine (PA) derivatives as the side products. IR spectroscopic data provide evidence that the protonated EI is the chemical intermediate for the reaction. The reaction for the formation of EDA from EA and ammonia required stronger acidic sites in the mordenite channels for higher yield and selectivity.

Characterizations of MAPO-36 molecular sieve by solid-state n.m.r.

Abstract The structure of the MAPO-36 framework was studied by the 27 Al and 31 P magic angle spinning ( MAS ) n.m.r. technique. The change in the 27 Al chemical shift from the tetrahedral aluminum position to the octahedral aluminum position upon adsorption of water indicates a secondary coordination of water molecules to aluminum atoms in the framework. The spectral change was reversible. The 31 P MAS n.m.r. spectra also changed reversibly upon adsorption and desorption of water. A strong interaction of water molecules and phosphorus atoms was confirmed by a large enhancement of the signal by [ 1 H— 31 P] cross-polarization (CP) mode.

RECENT ADVANCES IN APPLICATIONS OF MULTINUCLEAR SOLID-STATE NMR TO HETEROGENEOUS CATALYSIS AND INORGANIC MATERIALS

Abstract The interface between heterogeneous catalysis and the science of inorganic materials and high-resolution solid-state NMR is recently an area of much activity. A wide variety of novel techniques in multinuclear solid-state NMR have provided attractive possibilities in the mechanistic studies in catalysis as well as the design of catalysts and functional materials. Current state-of-the-art topics, by means of significant multinuclear solid-state NMR techniques, were selected to illustrate the scope of applications to the studies in the field of heterogeneous catalysis and inorganic materials.