13 research outputs found
Experimental and Theoretical Study for Vapor Phase Aldol Condensation of Methyl Acetate and Formaldehyde over Alkali Metal Oxides Supported on SBA-15
Alkali
metal oxides supported on SBA-15, M/SBA-15 (M = Li, Na,
K, Rb, and Cs), prepared by the impregnation method were characterized
and tested for the aldol condensation of methyl acetate and formaldehyde
to methyl acrylate (MA). M/SBA-15 catalysts are active for the formation
of MA while the support is inert. The supported alkali metals react
with hydroxyl groups on SBA-15 by replacing the H atoms and generate
weak and medium basic sites. The latter plays an important role in
promoting the reaction. Coke formation results in deactivation of
Cs/SBA-15, and the deactivated catalyst can be regenerated by burning
off the coke. Two possible reaction pathways for the formation of
MA were explored using quantum calculations. The predicated activity
for M/SBA-15 is consistent with the experimental observations. A pathway
with adsorbed enol molecule as an intermediate was suggested to be
predominant for the formation of MA
Lithium Borohydride Ethylenediaminates: A Case Study of Solid-State LiBH<sub>4</sub>–Organic Amine Complexes
Nitrogen
(N) containing ligands, such as ammonia (NH<sub>3</sub>), hydrazine
(N<sub>2</sub>H<sub>4</sub>), and ethylenediamine (en),
can form a series of complexes with common features in crystal structures
and thermal behaviors by coordinating with LiBH<sub>4</sub>. Two newly
synthesized lithium borohydride ethylenediaminates were investigated
in this work. Through comparing the crystal structures of LiBH<sub>4</sub>–en, LiBH<sub>4</sub>–NH<sub>3</sub>, and LiBH<sub>4</sub>–N<sub>2</sub>H<sub>4</sub> complexes, similar coordination
environments of Li were observed in which they have the same Li/N
molar ratios. Meanwhile, the establishment of dihydrogen bonding networks,
together with the Li<sup>+</sup>/N containing ligand interactions,
may be important reasons for the structural stabilization and are
expected to have profound impacts on their thermal behaviors. When
heated under Ar flow, LiBH<sub>4</sub>–N containing
complexes decompose via desorption of N containing ligands followed
by dehydrogenation. The coordination strength is affected by the number
of ligands, i.e., with the increase of N/Li ratio the
ligands can be released more easily. For dehydrogenation, the complex
with the shortest NH···HB distance gave rise to the
lowest initial temperature. When heated
in a closed system, direct dehydrogenation can be achieved at relatively
low temperatures with Co-based catalyst. About 8.5 and 7.7 wt % of
hydrogen can be released from Co-catalyzed LiBH<sub>4</sub>·en
and (LiBH<sub>4</sub>)<sub>2</sub>·en at 180
°C, respectively
Barium Hydride-Mediated Nitrogen Transfer and Hydrogenation for Ammonia Synthesis: A Case Study of Cobalt
Industrial
ammonia synthesis catalyzed by Fe- and Ru-based catalysts
is an energy-consuming process. The development of low-temperature
active catalyst has been pursued for a century. Herein, we report
that barium hydride (BaH<sub>2</sub>) can synergize with Co, leading
to a much better low-temperature activity, i.e., the BaH<sub>2</sub>-Co/carbon nanotube (CNT) catalyst exhibits ammonia synthesis activity
right above 150 °C; at 300 °C, it is 2 orders of magnitude
higher than that of the BaO-Co/CNTs and more than 2.5-times higher
than Cs-promoted Ru/MgO. Kinetic analyses reveal that the dissociative
adsorption of N<sub>2</sub> on the Co-BaH<sub>2</sub> catalyst may
not be the rate-determining step, as evidenced by the much smaller
reaction order of N<sub>2</sub> (0.43) and the lower apparent activation
energy (58 kJ mol<sup>–1</sup>) compared with those of the
unpromoted and BaO-promoted Co-based catalysts. BaH<sub>2</sub>, with
a negative hydride ion, may act as a strong reducing agent, removing
activated N from the Co surface and forming a BaNH species. The hydrogenation
of the BaNH species to NH<sub>3</sub> and BaH<sub>2</sub> can be facilely
carried out at 150 °C. The relayed catalysis by Co and BaH<sub>2</sub> sites creates an energy-favored pathway that allows ammonia
synthesis under milder conditions
Atomically Dispersed Pt on the Surface of Ni Particles: Synthesis and Catalytic Function in Hydrogen Generation from Aqueous Ammonia–Borane
The development of
cost-effective and highly efficient catalysts
is of scientific importance and practical need in the conversion and
utilization of clean energy. One of the strategies fulfilling that
demand is to achieve high exposure of a catalytically functional noble
metal to reactants to maximize its utilization efficiency. We report
herein that the single-atom alloy (SAA) made of atomically dispersed
Pt on the surface of Ni particles (Pt is surrounded by Ni atoms) exhibits
improved catalytic activity on the hydrolytic dehydrogenation of ammonia–borane,
a promising hydrogen storage method for onboard applications. Specifically,
an addition of 160 ppm of Pt leads to ca. 3-fold activity improvement
in comparison to that of pristine Ni/CNT catalyst. The turnover frequency
based on the isolated Pt is 12000 mol<sub>H2</sub> mol<sub>Pt</sub><sup>–1</sup> min<sup>–1</sup>, which is about 21 times
the value of the best Pt-based catalyst ever reported. Our simulation
results indicate that the high activity achieved stems from the synergistic
effect between Pt and Ni, where the negatively charged Pt (Pt<sup>δ‑</sup>) and positively charged Ni (Ni<sup>δ+</sup>) in the Pt-Ni alloy are prone to interact with H and OH of H<sub>2</sub>O molecules, respectively, leading to an energetically favorable
reaction pathway
Transition Metal-Free Hydrogenolysis of Anilines to Arenes Mediated by Lithium Hydride
Hydrodenitrogenation
(HDN) of nitrogen-containing organic compounds
such as aniline and its derivatives is of scientific interest and
practical importance. Major efforts have been devoted to the development
and understanding of transition metal-mediated chemical processes.
Herein, we report a fundamentally different strategy using a transition
metal-free material, that is, lithium hydride (LiH) enabling the hydrogenolysis
of aniline to benzene and ammonia via a chemical looping approach.
Aniline reacts with LiH to form lithium anilide, and subsequently,
the hydrogenolysis of lithium anilide yields benzene and ammonia and
regenerates LiH to complete the loop. This LiH-mediated chemical looping
HDN process stands in sharp contrast to the transition metal-catalyzed
or -mediated processes, which commonly lead to the complete hydrogenation
of aromatic rings. A highly denitrogenated product formation rate
of 2623 μmol·g–1·h–1 is achieved for the hydrogenolysis of lithium anilide at 300 °C
and 10 bar H2, which exceeds the catalytic rate of transition
metal catalysts. Computational studies reveal that the scission of
C–N bonds is facilitated by a Li-mediated nucleophilic attack
of hydride to the α-sp2C atom of aniline. This work
not only provides a distinctive chemical looping route for HDN, but
also opens up materials space for the denitrogenation of anilines
Image_5_Diversification of Sinorhizobium populations associated with Medicago polymorpha and Medicago lupulina in purple soil of China.JPEG
The double selection of environment adaptation and host specificity forced the diversification of rhizobia in nature. In the tropical region of China, Medicago polymorpha and Medicago lupulina are widely distributed, particularly in purple soil. However, the local distribution and diversity of rhizobia associated with these legumes has not been systematically investigated. To this end, root nodules of M. polymorpha and M. lupulina grown in purple soil at seven locations in Yunnan Province of China were collected for rhizobial isolation. The obtained rhizobia were characterized by RFLP of 16S–23S rRNA intergenic spacer, BOXAIR fingerprinting, and phylogeny of housekeeping and symbiosis genes. As result, a total of 91 rhizobial strains were classified into species Sinorhizobium medicae and S. meliloti, while three nodC gene types were identified among them. S. medicae containing nodC of type I was dominant in farmlands associated with M. polymorpha; while S. meliloti harboring nodC of type III was dominant in wild land nodulated by M. lupulina. For both rhizobial species, greater genetic diversity was detected in the populations isolated from their preferred host plant. A high level of genetic differentiation was observed between the two Sinorhizobium species, and gene flow was evident within the populations of the same species derived from different soil types, indicating that rhizobial evolution is likely associated with the soil features. To examine the effects of environmental features on rhizobial distribution, soil physicochemical traits and rhizobial genotypes were applied for constrained analysis of principle coordinates, which demonstrated that soil features like pH, nitrogen and sodium were the principle factors governing the rhizobial geographical distribution. Altogether, both S. medicae and S. meliloti strains could naturally nodulate with M. polymorpha and M. lupulina, but the rhizobium-legume symbiosis compatibility determined by both the host species and soil factors was also highlighted.</p
Image_7_Diversification of Sinorhizobium populations associated with Medicago polymorpha and Medicago lupulina in purple soil of China.JPEG
The double selection of environment adaptation and host specificity forced the diversification of rhizobia in nature. In the tropical region of China, Medicago polymorpha and Medicago lupulina are widely distributed, particularly in purple soil. However, the local distribution and diversity of rhizobia associated with these legumes has not been systematically investigated. To this end, root nodules of M. polymorpha and M. lupulina grown in purple soil at seven locations in Yunnan Province of China were collected for rhizobial isolation. The obtained rhizobia were characterized by RFLP of 16S–23S rRNA intergenic spacer, BOXAIR fingerprinting, and phylogeny of housekeeping and symbiosis genes. As result, a total of 91 rhizobial strains were classified into species Sinorhizobium medicae and S. meliloti, while three nodC gene types were identified among them. S. medicae containing nodC of type I was dominant in farmlands associated with M. polymorpha; while S. meliloti harboring nodC of type III was dominant in wild land nodulated by M. lupulina. For both rhizobial species, greater genetic diversity was detected in the populations isolated from their preferred host plant. A high level of genetic differentiation was observed between the two Sinorhizobium species, and gene flow was evident within the populations of the same species derived from different soil types, indicating that rhizobial evolution is likely associated with the soil features. To examine the effects of environmental features on rhizobial distribution, soil physicochemical traits and rhizobial genotypes were applied for constrained analysis of principle coordinates, which demonstrated that soil features like pH, nitrogen and sodium were the principle factors governing the rhizobial geographical distribution. Altogether, both S. medicae and S. meliloti strains could naturally nodulate with M. polymorpha and M. lupulina, but the rhizobium-legume symbiosis compatibility determined by both the host species and soil factors was also highlighted.</p
Table_1_Diversification of Sinorhizobium populations associated with Medicago polymorpha and Medicago lupulina in purple soil of China.XLSX
The double selection of environment adaptation and host specificity forced the diversification of rhizobia in nature. In the tropical region of China, Medicago polymorpha and Medicago lupulina are widely distributed, particularly in purple soil. However, the local distribution and diversity of rhizobia associated with these legumes has not been systematically investigated. To this end, root nodules of M. polymorpha and M. lupulina grown in purple soil at seven locations in Yunnan Province of China were collected for rhizobial isolation. The obtained rhizobia were characterized by RFLP of 16S–23S rRNA intergenic spacer, BOXAIR fingerprinting, and phylogeny of housekeeping and symbiosis genes. As result, a total of 91 rhizobial strains were classified into species Sinorhizobium medicae and S. meliloti, while three nodC gene types were identified among them. S. medicae containing nodC of type I was dominant in farmlands associated with M. polymorpha; while S. meliloti harboring nodC of type III was dominant in wild land nodulated by M. lupulina. For both rhizobial species, greater genetic diversity was detected in the populations isolated from their preferred host plant. A high level of genetic differentiation was observed between the two Sinorhizobium species, and gene flow was evident within the populations of the same species derived from different soil types, indicating that rhizobial evolution is likely associated with the soil features. To examine the effects of environmental features on rhizobial distribution, soil physicochemical traits and rhizobial genotypes were applied for constrained analysis of principle coordinates, which demonstrated that soil features like pH, nitrogen and sodium were the principle factors governing the rhizobial geographical distribution. Altogether, both S. medicae and S. meliloti strains could naturally nodulate with M. polymorpha and M. lupulina, but the rhizobium-legume symbiosis compatibility determined by both the host species and soil factors was also highlighted.</p
Image_3_Diversification of Sinorhizobium populations associated with Medicago polymorpha and Medicago lupulina in purple soil of China.JPEG
The double selection of environment adaptation and host specificity forced the diversification of rhizobia in nature. In the tropical region of China, Medicago polymorpha and Medicago lupulina are widely distributed, particularly in purple soil. However, the local distribution and diversity of rhizobia associated with these legumes has not been systematically investigated. To this end, root nodules of M. polymorpha and M. lupulina grown in purple soil at seven locations in Yunnan Province of China were collected for rhizobial isolation. The obtained rhizobia were characterized by RFLP of 16S–23S rRNA intergenic spacer, BOXAIR fingerprinting, and phylogeny of housekeeping and symbiosis genes. As result, a total of 91 rhizobial strains were classified into species Sinorhizobium medicae and S. meliloti, while three nodC gene types were identified among them. S. medicae containing nodC of type I was dominant in farmlands associated with M. polymorpha; while S. meliloti harboring nodC of type III was dominant in wild land nodulated by M. lupulina. For both rhizobial species, greater genetic diversity was detected in the populations isolated from their preferred host plant. A high level of genetic differentiation was observed between the two Sinorhizobium species, and gene flow was evident within the populations of the same species derived from different soil types, indicating that rhizobial evolution is likely associated with the soil features. To examine the effects of environmental features on rhizobial distribution, soil physicochemical traits and rhizobial genotypes were applied for constrained analysis of principle coordinates, which demonstrated that soil features like pH, nitrogen and sodium were the principle factors governing the rhizobial geographical distribution. Altogether, both S. medicae and S. meliloti strains could naturally nodulate with M. polymorpha and M. lupulina, but the rhizobium-legume symbiosis compatibility determined by both the host species and soil factors was also highlighted.</p
Image_1_Diversification of Sinorhizobium populations associated with Medicago polymorpha and Medicago lupulina in purple soil of China.JPEG
The double selection of environment adaptation and host specificity forced the diversification of rhizobia in nature. In the tropical region of China, Medicago polymorpha and Medicago lupulina are widely distributed, particularly in purple soil. However, the local distribution and diversity of rhizobia associated with these legumes has not been systematically investigated. To this end, root nodules of M. polymorpha and M. lupulina grown in purple soil at seven locations in Yunnan Province of China were collected for rhizobial isolation. The obtained rhizobia were characterized by RFLP of 16S–23S rRNA intergenic spacer, BOXAIR fingerprinting, and phylogeny of housekeeping and symbiosis genes. As result, a total of 91 rhizobial strains were classified into species Sinorhizobium medicae and S. meliloti, while three nodC gene types were identified among them. S. medicae containing nodC of type I was dominant in farmlands associated with M. polymorpha; while S. meliloti harboring nodC of type III was dominant in wild land nodulated by M. lupulina. For both rhizobial species, greater genetic diversity was detected in the populations isolated from their preferred host plant. A high level of genetic differentiation was observed between the two Sinorhizobium species, and gene flow was evident within the populations of the same species derived from different soil types, indicating that rhizobial evolution is likely associated with the soil features. To examine the effects of environmental features on rhizobial distribution, soil physicochemical traits and rhizobial genotypes were applied for constrained analysis of principle coordinates, which demonstrated that soil features like pH, nitrogen and sodium were the principle factors governing the rhizobial geographical distribution. Altogether, both S. medicae and S. meliloti strains could naturally nodulate with M. polymorpha and M. lupulina, but the rhizobium-legume symbiosis compatibility determined by both the host species and soil factors was also highlighted.</p