The challenges of solar hydrogen in chemical industry: how to provide, and how to apply?

Curbing anthropogenic CO2 emissions is one of the most important issues in the 21st century in order to mitigate climate change. Although the installation of solar cells for energy supply is in progress and these are becoming popular as an efficient use of sunlight, they are mostly used by energy-related industrial sectors. In the common chemical industry, various fossil resources are used to emit a huge amount of CO2. We believe that the chemical industry can make an effort to curb CO2 emissions by changing its resources to more environmentally benign ones. Solar hydrogen (hydrogen obtained by catalytic water splitting under sunlight) is an ideal sustainable resource and can be utilized as a chemical resource via combination with CO2. The 10 year program named "Artificial Photo Synthetic Chemical Process (ARPChem)" has been in progress under the support of the New Energy and Industrial Technology Development Organization (NEDO) in Japan since 2012. We introduce the strategy of ARPChem and the progress of the investigations including water splitting, hydrogen/oxygen separation, and olefin synthesis from solar hydrogen and CO2. We also argue that a realistic strategy to actualize "ARPChem" technologies in the society would be their combination with better fossil resources such as lower alkanes from a Life Cycle Assessment (LCA) point of view.

Framework stability and Brønsted acidity of isomorphously substituted interlayer-expanded zeolite COE-4: a density functional theory study.

COE-4 zeolites possess a unique two-dimensional ten-ring pore structure with the Si(OH)2 hydroxyl groups attached to the linker position between the ferrierite-type layers, which has been demonstrated through the interlayer-expansion approach in our previous work (H. Gies et al. Chem. Mater. 2012, 24, 1536). Herein, density functional theory is used to study the framework stability and Brønsted acidity of the zeolite T-COE-4, in which the tetravalent Si is isomorphously substituted by a trivalent Fe, B, Ga, or Al heteroatom at the linker position. The influences of substitution energy and equilibrium geometry parameters on the stability of T-COE-4 are investigated in detail. The relative acid strength of the linker position is revealed by the proton affinity, charge analysis, and NH3 adsorption. It is found that the range of the ⟨T-O-Si⟩ angles is widened to maintain the stability of isomorphously substituted T-COE-4 zeolites. The smaller the ⟨O1-T-O2⟩ bond angle is, the more difficult is to form the regular tetrahedral unit. Thus, the substitution energies at the linker positions increase in the following sequence: Al-COE-4 < Ga-COE-4 < Fe-COE-4 < B-COE-4. The adsorption of NH3 as a probe molecule indicates that the acidity can affect the hydrogen-bonding interaction between (N-H⋅⋅⋅O2) and (N⋅⋅⋅H-O2). The relative Brønsted-acid strength of the interlayer-expanded T-COE-4 zeolite decreases in the order of Al-COE-4 > Ga-COE-4 > Fe-COE-4 > B-COE-4. These findings may be helpful for the structural design and functional modification of interlayer-expanded zeolites.

Differences in Al distribution and acidic properties between RTH-type zeolites synthesized with OSDAs and without OSDAs.

In addition to the original preparation route of the RTH-type zeolites using 1,2,2,6,6-pentamethylpiperidine (PMP) as an organic structure directing agent (OSDA), we have found that simpler organic amines such as N-methylpiperidine and pyridine can be used as alternative OSDAs in place of PMP. Furthermore, we have established a synthesis method for preparing the RTH-type zeolites without using any OSDAs. In this study, RTH-type aluminosilicates were synthesized with different types of OSDA or without using any OSDAs. The obtained zeolites synthesized with different preparation methods were characterized by using various techniques, especially high-resolution (27)Al MAS NMR and in situ FT-IR techniques using CO adsorption. The relationship between the preparation method and the catalytic performance in the methanol to olefins (MTO) reaction was discussed. Finally, the distribution of Al species in the RTH-framework was clarified.

Preparation of a colloidal array of NaTaO3 nanoparticles via a confined space synthesis route and its photocatalytic application.

The confined space synthesis method has been applied to the preparation of sodium tantalate (NaTaO(3)); hydrothermal reaction of NaOH and Ta(2)O(5) was carried out in the pores of a three-dimensional mesoporous carbon, which was replicated by the colloidal array of silica nanospheres (SNSs) 20 nm in size. This approach led to the formation of a colloidal array of NaTaO(3) nanoparticles 20 nm in size with a surface area of 34 m(2) g(-1). The photocatalytic performance of the colloidal array of NaTaO(3) nanoparticles for overall water splitting under UV irradiation (λ > 200 nm) was evaluated after loading a NiO cocatalyst onto NaTaO(3) samples. The NiO-loaded NaTaO(3) nanoparticles showed photocatalytic activity for overall water splitting more than three times as high as non-structured bulk NaTaO(3) particles.

The influence of acidities of boron- and aluminium-containing MFI zeolites on co-reaction of methanol and ethene.

A series of boron- and aluminium-containing MFI zeolites were synthesized and various characterization techniques, such as NMR ((27)Al, (29)Si and (11)B), were employed to study the acidities of zeolites. Moreover, in situ IR was applied to investigate the interaction of methanol and ethene with the acid sites, and those catalytic materials were used for co-reaction of methanol and ethene to produce propene. The production of propene was related to the Al content of the zeolites with Si/Al ratios of higher than 90. It is implied that the presence of boron during the synthesis directed the aluminium to occupy certain tetrahedral sites in the zeolite framework, thus preventing the formation of ethene oligomers, and resulting in increased propene selectivity.

A comparative IR characterization of acidic sites on HY zeolite by pyridine and CO probes with silica-alumina and γ-alumina references.

Using IR spectroscopy, three different surface states of HY zeolite were probed by successive adsorption of CO at 143 K followed by evacuation and pyridine adsorption at 523 K: HY zeolite [1] without strong Lewis acid sites (LAS); [2] after high temperature (873 K) evacuation to convert Brønsted acid sites (BAS) to strong LAS; and [3] after water re-adsorption on HY zeolite [2] to recover BAS from LAS. The original surface of HY zeolite [1] seemed to be recovered on HY zeolite [3] after high temperature evacuation and water treatment by CO adsorption, while a part of generated LAS on HY zeolite [2] seemed irreversible on HY zeolite [3] to HY zeolite [1] by pyridine adsorption. To clarify this discrepancy, re-examination of the IR spectra of adsorbed CO and pyridine on γ-alumina and silica-alumina after similar treatments to those on HY zeolite was conducted. Based on the results of CO adsorption on γ-alumina and silica-alumina, the presence of extra-framework aluminium sites on HY zeolite [1] was confirmed. High temperature evacuation of HY zeolite [1] formed very strong LAS, a part of which was irreversible to BAS by water re-adsorption at room temperature. The irreversible sites on HY zeolite [3] were assigned to non-acidic OH groups attributed to silica-alumina. The non-acidic OH groups on HY zeolite [3], which were BAS on HY zeolite [1], hydrogen-bonded to pyridine to show IR spectra similar to those adsorbed on LAS. Thus, LAS on HY zeolite [3] seemed irreversible by pyridine adsorption after water re-adsorption. On the other hand, CO adsorbed on non-acidic OH groups showed a band at only slightly lower frequency (2160 cm(-1)) than that of BAS (2178 cm(-1)), resulting in overlapps and ignoring their presence. Thus, CO adsorption seemed to show that complete recovery of LAS to BAS occurred.

Synthesis and characterization of chiral mesoporous silica.

Chirality is widely expressed in organic materials, perhaps most notably in biological molecules such as DNA, and in proteins, owing to the homochirality of their components (d-sugars and l-amino acids). But the occurrence of large-scale chiral pores in inorganic materials is rare. Although some progress has been made in strategies to synthesize helical and chiral zeolite-like materials, the synthesis of enantiomerically pure mesoporous materials is a challenge that remains unsolved. Here we report the surfactant-templated synthesis of ordered chiral mesoporous silica, together with a general approach for the structural analysis of chiral mesoporous crystals by electron microscopy. The material that we have synthesized has a twisted hexagonal rod-like morphology, with diameter 130-180 nm and length 1-6 micro m. Transmission electron microscopy combined with computer simulations confirm the presence of hexagonally ordered chiral channels of 2.2 nm diameter winding around the central axis of the rods. Our findings could lead to new uses for mesoporous silica and other chiral pore materials in, for example, catalysis and separation media, where both shape selectivity and enantioselectivity can be applied to the manufacturing of enantiomerically pure chemicals and pharmaceuticals.

Vapor-phase silylation for the construction of monomeric silica puncheons in the interlayer micropores of Al-MWW layered precursor.

Vapor-phase silylation of Al-MWW layered precursor with SiMe(2)Cl(2) and following calcination produced an interlayer-expanded MWW structure with 12-membered ring micropores without delamination as a result of the formation of silica puncheons between the MWW sheets; strong acidity of zeolitic nature was retained.

Synthesis, crystallization mechanism, and catalytic properties of titanium-rich TS-1 free of extraframework titanium species.

A new route to the synthesis of TS-1 has been developed using (NH4)2CO3 as a crystallization-mediating agent. In this way, the framework Ti content can be significantly increased without forming extraframework Ti species. The prepared catalyst had a Si/Ti ratio as low as 34 in contrast to the ratio of 58 achieved with the methods A and B established by the Enichem group (Clerici, M. G.; Bellussi, G.; Romano, U. J. Catal. 1991, 129, 159) and Thangaraj and Sivasanker (Thangaraj, A.; Sivasanker, S. J. Chem. Soc., Chem. Commun. 1992, 123), respectively. The material contained less defect sites than the samples synthesized by the other two methods. As a result, it showed much higher activity for the oxidation of various organic substrates, such as linear alkanes/alkenes and alcohols, styrene, and benzene. The crystallization mechanism of TS-1 in the presence of (NH4)2CO3 was studied by following the whole crystallization process with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetry/differential thermal analysis (TG/DTA), inductively coupled plasma atomic emission spectrometry (ICP), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-vis spectroscopy, and (29)Si MAS (magic-angle spinning) NMR spectroscopy techniques. It was shown that the presence of (NH4)2CO3 not only drastically lowered down pH, slowing down the crystallization process and making the incorporation of Ti into the framework match well with nucleation and crystal growth, but also modified the crystallization mechanism. It seems that the solid-phase transformation mechanism predominated in the crystallization process initiated by dissociation, reorganization, and recoalescence of the solidified gel although a small amount of nongelatinated Ti shifted to the solid during the crystal growth period. In contrast, a typical homogeneous nucleation mechanism occurred in the method A system. Thus, although in the method A system most of Ti cations was inserted into the lattice after the crystallization was nearly completed, the inclusion of Ti started at the earlier nucleation period in the presence of (NH4)2CO3. This is favorable for the incorporation of Ti into the framework, resulting in a more homogeneous distribution of Ti in the framework. Oxidation of 1-hexene and 2-hexanol over the samples collected during the whole crystallization process indicated that condensation of Ti-OH and Si-OH proceeded even after the crystallization was completed. This resulted in an increase in hydrophobicity and an overall improvement in microscopic character of Ti species and consequently a great increase in the catalytic activity with further progress of crystallization.

Methodology for synthesizing crystalline metallosilicates with expanded pore windows through molecular alkoxysilylation of zeolitic lamellar precursors.

Postalkoxysilylation with diethoxydimethylsilane has been carried out on the zeolitic lamellar precursors of various topologies such as MWW, FER, CDO and MCM-47 aiming to construct new crystalline structures with expanded pore apertures between the layers. The silylation process and the crystalline and pore structures of the resulting materials have been investigated with the techniques of XRD, IR, (13)C and (29)Si MAS NMR, ICP, SEM, HRTEM, elemental analyses, and N 2 adsorption. In contrast to forming known three-dimensional zeolite structures after direct calcination of the lamellar precursors, the silylation led to new crystalline structures with opener pores, as evidenced by the shift of layer-related diffractions to the lower-angle region in XRD patterns and the enlarged interlayer pores found by HRTEM images. After optimizing the treatment conditions, particularly the amount of silane agent, a maximum and homogeneous silylation was realized, which guaranteed the phase purity in interlayer expanded zeolites. The expanded structures were well preserved after calcination at 823 K or reflux in water for 1 to 2 weeks, indicating a high thermal stability and also a hydrothermal stability. The interlayer expanded zeolites prepared from the metallosilicate precursors of MWW topology exhibited higher catalytic activities in the redox and solid acid-catalyzed reactions of bulky molecules than that of their counterparts with conventional MWW topology.

Synthesis and catalytic performance of Ti-MCM-68 for effective oxidation reactions.

Microporous titanosilicate Ti-MCM-68 (Ti-MSE) was successfully synthesized by post-synthetic isomorphous substitution of Ti for Al and proved to be a high-performance catalyst, in particular showing superior performance to TS-1, Ti-BEA, and Ti-MWW for phenol oxidation using H(2)O(2) as an oxidant.

Activation of hydrocarbons on acidic zeolites: superior selectivity of methylation of ethene with methanol to propene on weakly acidic catalysts.

The study of methylation of ethene with methanol to propene over MFI zeolites with different heteroatoms has found that an efficient catalyst with weak acidities prevented the side reactions related with the formation of ethene oligomers from occurring, as evidenced by in situ IR spectroscopy, leading to superior propene selectivity in the product distribution.

Liquid phase separation of 1-butene from 2-butenes on all-silica zeolite RUB-41.

The all-silica zeolite RUB-41, containing 8- and 10-membered rings, is able to separate trans-2-butene and cis-2-butene from 1-butene and represents a possible improvement in isolating pure 1-butene from a butene mixture.

Solid-state 13C NMR studies on organic-inorganic hybrid zeolites.

A novel type of organic-inorganic hybrid zeolite with organic lattice (ZOL) is studied in detail by solid-state (13)C magic angle spinning nuclear magnetic resonance (MAS NMR). The (13)C MAS NMR measurements employing several pulse sequences quantitatively demonstrate that methylene groups are really incorporated in the framework, although they are partially cleaved into methyl groups. The organic species in ZOL materials are open for adsorbates, which is evidenced by the (13)C MAS NMR measurements for an n-hexane-adsorbing ZOL material. This finding strongly suggests that organic moieties are incorporated as a zeolite framework, indicating that ZOL is not a physical mixture of a carbon-containing amorphous aggregate and a conventional zeolite but a true organic-inorganic hybrid zeolite.

Unique adsorption properties of organic-inorganic hybrid zeolite IEZ-1 with dimethylsilylene moieties.

The interlayer silylation of pure silica PLS-1 with dichlorodimethylsilane gave a novel organic-inorganic hybrid zeolite IEZ-1, of which the micropores are able to adsorb benzene molecules, in contrast to its purely inorganic analogue IEZ-2.

Synthesis of crystallized mesoporous transition metal oxides by silicone treatment of the oxide precursor.

Ordered mesoporous transition metal oxides were successfully crystallized after strengthening the amorphous framework by a silica layer, which efficiently protected the original mesoporous structure against crystallization and resulting mass transfer.

Mechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5.

The reaction mechanism of the decomposition of ethoxy species to ethene and acidic OH groups on H-ZSM-5 was studied by IR spectroscopy using isotope-labeled ethanol. The concerted mechanism occurring on both the ethoxy (acid) site and the counterpart lattice oxygen was suggested by GC-MS analysis of evolved d2-ethene and IR observation of the recovery of OH s groups on acid sites from the decomposition of CH3CD2O- ethoxy species. The concerted mechanism was further confirmed by the estimation of activation energy for decomposition of CH3CH2O-, CH3CD2O-, and CD3CD2O- ethoxy species, 122 ± 3, 125 ± 3, and 140 ± 5 kJ mol(-1), respectively, where the kinetic isotope effect was observed for the cleavage of the CH or CD bond of the methyl group of the ethoxy species.

Titanium(IV) in the organic-structure-directing-agent-free synthesis of hydrophobic and large-pore molecular sieves as redox catalysts.

Titanium(IV) incorporated into the framework of molecular sieves can be used as a highly active and sustainable catalyst for the oxidation of industrially important organic molecules. Unfortunately, the current process for the incorporation of titanium(IV) requires a large amount of expensive organic molecules used as organic-structure-directing agents (OSDAs), and this significantly increases the production costs and causes environmental problems owing to the removal of OSDAs by pyrolysis. Herein, an OSDA-free process was developed to incorporate titanium(IV) into BEA-type molecular sieves for the first time. More importantly, the hydrophobic environment and the robust, 3 D, and large pore structure of the titanium(IV)-incorporated molecular sieves fabricated from the OSDA-free process created a catalyst that was extremely active and selective for the epoxidation of bulky cyclooctene in comparison to Ti-incorporated BEA-type molecular sieves synthesized with OSDAs and commercial titanosilicate TS-1.