ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, ... more Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, Fe, Co, Ni, and Cu supported on anatase TiO 2 has been studied. Among the catalysts tested, Mn/TiO 2 supported on Hombikat TiO 2 provided the best performance with 100% N 2 selectivity and complete NO conversion at temperatures as low as 393 K under numerous conditions. The catalytic performance for various transition metal oxides supported on TiO 2 decreased in the following order: Mn > Cu Cr Co > Fe V ≫ Ni. For Mn-based catalysts the activity increases with an increase in Mn loading and the reaction temperature. TiO 2 alone did not give any NO conversion at 573 K, and calcination at low temperature ( 673 K) is preferable. XRD coupled with XPS confirmed the presence of MnO 2 as a major phase (peak at 642.2 eV) with Mn 2 O 3 , and partially undecomposed Mn-nitrate as the minor phases for supported manganese catalysts. It is proposed that MnO 2 contributes to the high activity of Mn/TiO 2 . XPS results also confirmed a higher concentration of active metal oxides on the surface of Mn/TiO 2 compared to the other catalysts. The NH 3 FT-IR study showed the presence of Lewis acid sites for the most active catalysts, while the peak corresponding to Brönsted acid sites was weak or absent. This strongly suggests that Brönsted acid sites are not necessary for the reaction to occur at low temperatures. The H 2 TPR study indicated the difficulty of reducing Mn oxide when the metal loading is low and/or the catalysts are calcined at temperatures higher than 773 K. It is concluded that lower catalyst calcination temperatures, Lewis acidity, the redox properties of metal oxides and their higher surface concentration are important for very high SCR activity at low temperatures. Mn/TiO 2 provided the best performance at 50,000 h −1 when the catalysts were tested in the presence of 11 vol% H 2 O. Under these conditions, the catalytic activity of the transition metal oxides decreases in the following order: Mn > V Co > Cu > Cr > Fe Ni.
Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, ... more Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, Fe, Co, Ni, and Cu supported on anatase TiO 2 has been studied. Among the catalysts tested, Mn/TiO 2 supported on Hombikat TiO 2 provided the best performance with 100% N 2 selectivity and complete NO conversion at temperatures as low as 393 K under numerous conditions. The catalytic performance for various transition metal oxides supported on TiO 2 decreased in the following order: Mn > Cu Cr Co > Fe V ≫ Ni. For Mn-based catalysts the activity increases with an increase in Mn loading and the reaction temperature. TiO 2 alone did not give any NO conversion at 573 K, and calcination at low temperature ( 673 K) is preferable. XRD coupled with XPS confirmed the presence of MnO 2 as a major phase (peak at 642.2 eV) with Mn 2 O 3 , and partially undecomposed Mn-nitrate as the minor phases for supported manganese catalysts. It is proposed that MnO 2 contributes to the high activity of Mn/TiO 2 . XPS results also confirmed a higher concentration of active metal oxides on the surface of Mn/TiO 2 compared to the other catalysts. The NH 3 FT-IR study showed the presence of Lewis acid sites for the most active catalysts, while the peak corresponding to Brönsted acid sites was weak or absent. This strongly suggests that Brönsted acid sites are not necessary for the reaction to occur at low temperatures. The H 2 TPR study indicated the difficulty of reducing Mn oxide when the metal loading is low and/or the catalysts are calcined at temperatures higher than 773 K. It is concluded that lower catalyst calcination temperatures, Lewis acidity, the redox properties of metal oxides and their higher surface concentration are important for very high SCR activity at low temperatures. Mn/TiO 2 provided the best performance at 50,000 h −1 when the catalysts were tested in the presence of 11 vol% H 2 O. Under these conditions, the catalytic activity of the transition metal oxides decreases in the following order: Mn > V Co > Cu > Cr > Fe Ni.
Low-Temperature Selective Catalytic Reduction (SCR) of NO with NH 3 by Using Mn, Cr, and Cu Oxide... more Low-Temperature Selective Catalytic Reduction (SCR) of NO with NH 3 by Using Mn, Cr, and Cu Oxides Supported on Hombikat TiO 2 .
TiO 2 -supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH 3 have been s... more TiO 2 -supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH 3 have been synthesized by wet impregnation. The adsorption and coadsorption of NH 3 , NO, and O 2 , in conjunction with in situ FT-IR spectroscopy, was used to elucidate the reaction mechanism as the samples were heated from 323 to 673 K. While Cr was the only transition metal that generated significant amounts of Brønsted acidity, strong Lewis acid sites were present over all of the materials. The peak strength corresponding to the δ s (NH 3 ) coordinated to Lewis acid sites decreased in the following order: Ti > Mn > Cr ∼ Cu. Similarly, the peak strength corresponding to the δ as (NH 3 ) coordinated to Lewis acid sites decreased as follows: Mn > Cr ∼ Cu. Exposing the catalysts to oxygen before the introduction of NO did not impact the adsorption of NO as nitrates on the catalysts, suggesting that labile lattice oxygen plays an important role in the formation of nitrates. Three types of nitrates were observed after the adsorption of NO. Monodentate and bidentate nitrates formed on the surface of all the materials tested, while bridged nitrates only formed on CrO x /TiO 2 . The in situ FTIR data collected resulted in the development of a reaction mechanism for MnO x /TiO 2 . A combination of moderately strong monodentate and bidentate nitrate species, along with a split in the symmetric deformation of NH 3 coordinated to Lewis acid sites, appear to be important for high activity and selectivity. The peak resulting from the vibrational mode of ammonia adsorbed on Lewis acid sites, which is located at ∼1170 cm -1 , is believed to be important in facilitating hydrogen abstraction to form amide species that react with bidentate nitrates (1620 cm -1 ). It is proposed that the reaction mechanism proceeds through the formation of nitrosamide and azoxy species, which most likely possess lifetimes as reaction intermediates that are too brief for detection. In contrast to MnO x /TiO 2 , the apparent participation of Brønsted acid sites for CrO x /TiO 2 suggests that a different reaction pathway is involved for this catalyst.
Gold supported on titanium-based metal oxides can assist the selective partial oxidation of propy... more Gold supported on titanium-based metal oxides can assist the selective partial oxidation of propylene at temperatures from 313 K to 573 K in a gas containing both H2 and O2. The preparation method was found to be crucial in controlling the selectivities. In general, impregnation and chemical vapor deposition methods do not produce selective catalysts. Only the deposition-precipitation method makes gold selective to propylene oxide or propanal, suggesting that a strong contact between the gold particles and the titanium ion sites on the support is important. The effect of changing the support was also dramatic; the use of the anatase form of TiO2 and Ti-MCM-41 results in propylene oxide production, while the rutile structure of TiO2 caused complete oxidation to CO2. Microporous crystalline titanium silicates such as TS-1, TS-2, and Ti-β zeolite make gold relatively selective to propanal and of the three TS-1 gives the highest selectivity. These results indicate that the oxidation of propylene in the copresence of H2 must involve the surface of the supports and that the reaction takes place at the interface perimeter around the gold particles.
Vapor-phase epoxidation of propylene to propylene oxide (PO) using H 2 and O 2 has been carried o... more Vapor-phase epoxidation of propylene to propylene oxide (PO) using H 2 and O 2 has been carried out over Au deposited on Ti-MCM-41 and TiO 2 -SiO 2 mixed oxides having various Ti/Si molar ratios ranging from 0.25/100 to 6.0/100. The Ti-MCM-41 supports were prepared by using two different structure-directing organic templates: dodecyltrimethylammonium hydroxide (C12TMACl) and cetyltrimethylammonium hydroxide (C16TMACl). TiO 2 -SiO 2 mixed oxides were prepared by a sol-gel process. Gold nano-particles were loaded by deposition-precipitation (DP) using various precipitating agents: LiOH, NaOH, KOH, RbOH, and CsOH. Au/Ti-MCM-41 gives increased propylene conversion with an increase in Ti/Si ratio and the PO yield passes through a maximum (conversion = 3.2%, PO selectivity = 93.5%) at 100 • C at a Ti/Si molar ratio of 3/100. However, at higher reaction temperatures of ≥120 • C, PO selectivity decreases with an increase in the Ti/Si ratio. At the reaction temperatures of 150 and 200 • C, to get better performance, the ideal catalysts should have Ti/Si ratios of 2/100 and 1.5/100, respectively. The critical balance among Ti-content, Au loading and the reaction temperature is important to achieve the higher propylene conversion, PO selectivity above 90% and lower H 2 (and O 2 ) consumption. Gold supported on TiO 2 -SiO 2 mixed oxides showed very poor performance, probably due to higher concentrations of extra framework titanium and lower dispersion of gold particles.
1 · cm −3 /g(cat.) and at reaction temperature of 100 or 150 • C. Influences of the various param... more 1 · cm −3 /g(cat.) and at reaction temperature of 100 or 150 • C. Influences of the various parameters investigated in the case of Ti-MCM-48 support are Si/Ti (30, 50, 75, and 100) ratios, precipitating agents (LiOH, NaOH, KOH, RbOH, or CsOH) for Au deposition, pH (6-8), Au loading (2-25 wt% in solution), and calcination temperature (150-500 • C). The supports were characterized by XRD, UVvis, FT-IR, and surface area measurements, whereas supported gold catalysts were characterized by TEM, ICP, and XPS techniques. Better performance was observed with Ti-MCM-48 (initial conversion = 5.6%, PO selectivity = 92%), due to its three-dimensional pore system, than with Ti-MCM-41 (initial conversion = 5.1%, PO selectivity = 88%) in the propene epoxidation at 150 • C. GC-MS investigation of the extracted species using organic solvent from the used catalyst revealed that acidic as well as oligomeric species accumulated on the catalyst surfaces. These species are assumed to cause the catalyst deactivation. Silylation of the catalyst Au/Ti-MCM-48 prohibits it from getting deactivated faster and also helps to improve PO selectivity and decrease H 2 consumption. Based on the above experimental results, a probable reaction mechanism is explained. c 2002 Elsevier Science (USA)
Steam reforming, CO2 reforming and simultaneous steam and CO2 reforming reactions of methane for ... more Steam reforming, CO2 reforming and simultaneous steam and CO2 reforming reactions of methane for its conversion into syngas (H2 and CO) over NiO/MgO/SA-5205 catalyst (prepared by depositing NiO on MgO precoated SA-5205 support) have been investigated at different process conditions. In some cases O2 was present in the feed, while in other cases it was not. The catalyst has been
Effects of titania on the catalytic property of Pd/Al 2 O 3 towards methane combustion were exami... more Effects of titania on the catalytic property of Pd/Al 2 O 3 towards methane combustion were examined. The results revealed that the catalytic activity of the Pd/Al 2 O 3 catalyst was considerably improved by pre-coating the alumina support with titania at low temperature (below 700 8C). Hydrogen chemisorption and BET measurements revealed that the titania-modified alumina supports could modify the support characterization to achieve a high dispersion of palladium. Temperature-programmed reduction and temperature-programmed desorption study further demonstrated that the coating of Pd/Al 2 O 3 catalysts with titania can weaken the bond strength of Pd-O and enhance their catalytic activity towards methane combustion at lower temperature. q
Methane-to-Câ-hydrocarbon conversion activity and selectivity (or yield) of MgO and La-promoted M... more Methane-to-Câ-hydrocarbon conversion activity and selectivity (or yield) of MgO and La-promoted MgO catalysts in the oxidative coupling of methane and strong basicity of the catalysts are decreased appreciably when these catalysts are deposited on commonly used commercial low surface area porous catalyst carriers containing AlâOâ, SiOâ, SiC, or ZrOâ + HfOâ as the main components. The decrease in the strong
Journal of Chemical Technology and Biotechnology, 1998
... Vasant R. Choudhary,; Shafeek AR Mulla,; Balu S. Uphade. Article first published online: 4 MA... more ... Vasant R. Choudhary,; Shafeek AR Mulla,; Balu S. Uphade. Article first published online: 4 MAY 1999. ... Publication History. Issue published online: 4 MAY 1999; Article first published online: 4 MAY 1999; Manuscript Accepted: 13 JAN 1998; Manuscript Revised: 26 SEP 1997; ...
Catalytic steam and oxysteam reforming of methane to syngas studied involves coupling of exotherm... more Catalytic steam and oxysteam reforming of methane to syngas studied involves coupling of exothermic oxidative conversion and endothermic steam-reforming processes over Cox Ni1−x O (x = 0.0–0.5) supported on MgO precoated commercial low surface area (<0.01 m2 g−1) macroporous silica-alumina SA-5205 catalyst carrier. The influence of the Co/Ni ratio of the catalyst on its performance in steam and oxysteam reforming processes (at 800 and 850°C) was studied. For the steam reforming process, the Co/Ni ratio influences strongly on the methane and steam conversion and CO selectivity and product H2/CO ratio, particularly at lower temperature. When the Co/Ni ratio is increased, the methane and H2 O conversion and CO selectivity are decreased markedly. For the oxysteam reforming process, the influence of the Co/Ni ratio on the performance is smaller and depends on process conditions. When the Co/Ni is increased, the methane conversion passes through a maximum at the Co/Ni ratio of 0.17. The influence of the reaction temperature (800 and 850°C) and CH4/O2 and CH4/H2 O ratios on the conversion, selectivity, H2/CO product ratio, and net reaction heat (ΔHr ) was studied in the oxysteam reforming (at space velocity of 47,000 cm3·g−1·h−1) over the catalyst with an optimum Co/Ni ratio (0.17) and a higher Co/Ni ratio (1.0). The oxysteam reforming process involves coupling the exothermic oxidative conversion of methane and the endothermic methane steam reforming reactions, making the process highly energy-efficient and nonhazardous. This process can be made thermoneutral, mildly exothermic, and mildly endothermic by manipulating process conditions.
Combustion of dilute toluene and methyl ethyl ketone over Mn-doped ZrO 2 catalysts prepared using... more Combustion of dilute toluene and methyl ethyl ketone over Mn-doped ZrO 2 catalysts prepared using different precipitating agents, such as tetra-alkyl ammonium hydroxides and NH 4 OH, having Mn/Zr ratios from 0.05 to 0.67, and calcined at different temperatures has been thoroughly investigated. The Mn-doped ZrO 2 catalyst shows high toluene or methyl ethyl ketone combustion activity, particularly when its ZrO 2 is in cubic form, when its Mn/Zr ratio is close to 0.2, and when it is prepared using tetra-methyl ammonium hydroxide as a precipitating agent and calcined at 773 K.
Oxidative coupling of methane (OCM) to ethylene and ethane is a futuristic process of great pract... more Oxidative coupling of methane (OCM) to ethylene and ethane is a futuristic process of great practical importance for the effective utilization of methane/natural gas. A brief summary of the work carried out at National Chemical Laboratory (Pune) for the development of catalyst and catalytic process for OCM, particularly addressing the major issues/limitations of the OCM process and efforts made to overcome the problems is presented. This review particularly covers the development of a number of highly active/selective and stable unsupported and supported (using commercial catalyst carriers) catalysts for the OCM process and also the process of improvements/modifications to overcome most of the limitations of OCM.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, ... more Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, Fe, Co, Ni, and Cu supported on anatase TiO 2 has been studied. Among the catalysts tested, Mn/TiO 2 supported on Hombikat TiO 2 provided the best performance with 100% N 2 selectivity and complete NO conversion at temperatures as low as 393 K under numerous conditions. The catalytic performance for various transition metal oxides supported on TiO 2 decreased in the following order: Mn > Cu Cr Co > Fe V ≫ Ni. For Mn-based catalysts the activity increases with an increase in Mn loading and the reaction temperature. TiO 2 alone did not give any NO conversion at 573 K, and calcination at low temperature ( 673 K) is preferable. XRD coupled with XPS confirmed the presence of MnO 2 as a major phase (peak at 642.2 eV) with Mn 2 O 3 , and partially undecomposed Mn-nitrate as the minor phases for supported manganese catalysts. It is proposed that MnO 2 contributes to the high activity of Mn/TiO 2 . XPS results also confirmed a higher concentration of active metal oxides on the surface of Mn/TiO 2 compared to the other catalysts. The NH 3 FT-IR study showed the presence of Lewis acid sites for the most active catalysts, while the peak corresponding to Brönsted acid sites was weak or absent. This strongly suggests that Brönsted acid sites are not necessary for the reaction to occur at low temperatures. The H 2 TPR study indicated the difficulty of reducing Mn oxide when the metal loading is low and/or the catalysts are calcined at temperatures higher than 773 K. It is concluded that lower catalyst calcination temperatures, Lewis acidity, the redox properties of metal oxides and their higher surface concentration are important for very high SCR activity at low temperatures. Mn/TiO 2 provided the best performance at 50,000 h −1 when the catalysts were tested in the presence of 11 vol% H 2 O. Under these conditions, the catalytic activity of the transition metal oxides decreases in the following order: Mn > V Co > Cu > Cr > Fe Ni.
Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, ... more Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, Fe, Co, Ni, and Cu supported on anatase TiO 2 has been studied. Among the catalysts tested, Mn/TiO 2 supported on Hombikat TiO 2 provided the best performance with 100% N 2 selectivity and complete NO conversion at temperatures as low as 393 K under numerous conditions. The catalytic performance for various transition metal oxides supported on TiO 2 decreased in the following order: Mn > Cu Cr Co > Fe V ≫ Ni. For Mn-based catalysts the activity increases with an increase in Mn loading and the reaction temperature. TiO 2 alone did not give any NO conversion at 573 K, and calcination at low temperature ( 673 K) is preferable. XRD coupled with XPS confirmed the presence of MnO 2 as a major phase (peak at 642.2 eV) with Mn 2 O 3 , and partially undecomposed Mn-nitrate as the minor phases for supported manganese catalysts. It is proposed that MnO 2 contributes to the high activity of Mn/TiO 2 . XPS results also confirmed a higher concentration of active metal oxides on the surface of Mn/TiO 2 compared to the other catalysts. The NH 3 FT-IR study showed the presence of Lewis acid sites for the most active catalysts, while the peak corresponding to Brönsted acid sites was weak or absent. This strongly suggests that Brönsted acid sites are not necessary for the reaction to occur at low temperatures. The H 2 TPR study indicated the difficulty of reducing Mn oxide when the metal loading is low and/or the catalysts are calcined at temperatures higher than 773 K. It is concluded that lower catalyst calcination temperatures, Lewis acidity, the redox properties of metal oxides and their higher surface concentration are important for very high SCR activity at low temperatures. Mn/TiO 2 provided the best performance at 50,000 h −1 when the catalysts were tested in the presence of 11 vol% H 2 O. Under these conditions, the catalytic activity of the transition metal oxides decreases in the following order: Mn > V Co > Cu > Cr > Fe Ni.
Low-Temperature Selective Catalytic Reduction (SCR) of NO with NH 3 by Using Mn, Cr, and Cu Oxide... more Low-Temperature Selective Catalytic Reduction (SCR) of NO with NH 3 by Using Mn, Cr, and Cu Oxides Supported on Hombikat TiO 2 .
TiO 2 -supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH 3 have been s... more TiO 2 -supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH 3 have been synthesized by wet impregnation. The adsorption and coadsorption of NH 3 , NO, and O 2 , in conjunction with in situ FT-IR spectroscopy, was used to elucidate the reaction mechanism as the samples were heated from 323 to 673 K. While Cr was the only transition metal that generated significant amounts of Brønsted acidity, strong Lewis acid sites were present over all of the materials. The peak strength corresponding to the δ s (NH 3 ) coordinated to Lewis acid sites decreased in the following order: Ti > Mn > Cr ∼ Cu. Similarly, the peak strength corresponding to the δ as (NH 3 ) coordinated to Lewis acid sites decreased as follows: Mn > Cr ∼ Cu. Exposing the catalysts to oxygen before the introduction of NO did not impact the adsorption of NO as nitrates on the catalysts, suggesting that labile lattice oxygen plays an important role in the formation of nitrates. Three types of nitrates were observed after the adsorption of NO. Monodentate and bidentate nitrates formed on the surface of all the materials tested, while bridged nitrates only formed on CrO x /TiO 2 . The in situ FTIR data collected resulted in the development of a reaction mechanism for MnO x /TiO 2 . A combination of moderately strong monodentate and bidentate nitrate species, along with a split in the symmetric deformation of NH 3 coordinated to Lewis acid sites, appear to be important for high activity and selectivity. The peak resulting from the vibrational mode of ammonia adsorbed on Lewis acid sites, which is located at ∼1170 cm -1 , is believed to be important in facilitating hydrogen abstraction to form amide species that react with bidentate nitrates (1620 cm -1 ). It is proposed that the reaction mechanism proceeds through the formation of nitrosamide and azoxy species, which most likely possess lifetimes as reaction intermediates that are too brief for detection. In contrast to MnO x /TiO 2 , the apparent participation of Brønsted acid sites for CrO x /TiO 2 suggests that a different reaction pathway is involved for this catalyst.
Gold supported on titanium-based metal oxides can assist the selective partial oxidation of propy... more Gold supported on titanium-based metal oxides can assist the selective partial oxidation of propylene at temperatures from 313 K to 573 K in a gas containing both H2 and O2. The preparation method was found to be crucial in controlling the selectivities. In general, impregnation and chemical vapor deposition methods do not produce selective catalysts. Only the deposition-precipitation method makes gold selective to propylene oxide or propanal, suggesting that a strong contact between the gold particles and the titanium ion sites on the support is important. The effect of changing the support was also dramatic; the use of the anatase form of TiO2 and Ti-MCM-41 results in propylene oxide production, while the rutile structure of TiO2 caused complete oxidation to CO2. Microporous crystalline titanium silicates such as TS-1, TS-2, and Ti-β zeolite make gold relatively selective to propanal and of the three TS-1 gives the highest selectivity. These results indicate that the oxidation of propylene in the copresence of H2 must involve the surface of the supports and that the reaction takes place at the interface perimeter around the gold particles.
Vapor-phase epoxidation of propylene to propylene oxide (PO) using H 2 and O 2 has been carried o... more Vapor-phase epoxidation of propylene to propylene oxide (PO) using H 2 and O 2 has been carried out over Au deposited on Ti-MCM-41 and TiO 2 -SiO 2 mixed oxides having various Ti/Si molar ratios ranging from 0.25/100 to 6.0/100. The Ti-MCM-41 supports were prepared by using two different structure-directing organic templates: dodecyltrimethylammonium hydroxide (C12TMACl) and cetyltrimethylammonium hydroxide (C16TMACl). TiO 2 -SiO 2 mixed oxides were prepared by a sol-gel process. Gold nano-particles were loaded by deposition-precipitation (DP) using various precipitating agents: LiOH, NaOH, KOH, RbOH, and CsOH. Au/Ti-MCM-41 gives increased propylene conversion with an increase in Ti/Si ratio and the PO yield passes through a maximum (conversion = 3.2%, PO selectivity = 93.5%) at 100 • C at a Ti/Si molar ratio of 3/100. However, at higher reaction temperatures of ≥120 • C, PO selectivity decreases with an increase in the Ti/Si ratio. At the reaction temperatures of 150 and 200 • C, to get better performance, the ideal catalysts should have Ti/Si ratios of 2/100 and 1.5/100, respectively. The critical balance among Ti-content, Au loading and the reaction temperature is important to achieve the higher propylene conversion, PO selectivity above 90% and lower H 2 (and O 2 ) consumption. Gold supported on TiO 2 -SiO 2 mixed oxides showed very poor performance, probably due to higher concentrations of extra framework titanium and lower dispersion of gold particles.
1 · cm −3 /g(cat.) and at reaction temperature of 100 or 150 • C. Influences of the various param... more 1 · cm −3 /g(cat.) and at reaction temperature of 100 or 150 • C. Influences of the various parameters investigated in the case of Ti-MCM-48 support are Si/Ti (30, 50, 75, and 100) ratios, precipitating agents (LiOH, NaOH, KOH, RbOH, or CsOH) for Au deposition, pH (6-8), Au loading (2-25 wt% in solution), and calcination temperature (150-500 • C). The supports were characterized by XRD, UVvis, FT-IR, and surface area measurements, whereas supported gold catalysts were characterized by TEM, ICP, and XPS techniques. Better performance was observed with Ti-MCM-48 (initial conversion = 5.6%, PO selectivity = 92%), due to its three-dimensional pore system, than with Ti-MCM-41 (initial conversion = 5.1%, PO selectivity = 88%) in the propene epoxidation at 150 • C. GC-MS investigation of the extracted species using organic solvent from the used catalyst revealed that acidic as well as oligomeric species accumulated on the catalyst surfaces. These species are assumed to cause the catalyst deactivation. Silylation of the catalyst Au/Ti-MCM-48 prohibits it from getting deactivated faster and also helps to improve PO selectivity and decrease H 2 consumption. Based on the above experimental results, a probable reaction mechanism is explained. c 2002 Elsevier Science (USA)
Steam reforming, CO2 reforming and simultaneous steam and CO2 reforming reactions of methane for ... more Steam reforming, CO2 reforming and simultaneous steam and CO2 reforming reactions of methane for its conversion into syngas (H2 and CO) over NiO/MgO/SA-5205 catalyst (prepared by depositing NiO on MgO precoated SA-5205 support) have been investigated at different process conditions. In some cases O2 was present in the feed, while in other cases it was not. The catalyst has been
Effects of titania on the catalytic property of Pd/Al 2 O 3 towards methane combustion were exami... more Effects of titania on the catalytic property of Pd/Al 2 O 3 towards methane combustion were examined. The results revealed that the catalytic activity of the Pd/Al 2 O 3 catalyst was considerably improved by pre-coating the alumina support with titania at low temperature (below 700 8C). Hydrogen chemisorption and BET measurements revealed that the titania-modified alumina supports could modify the support characterization to achieve a high dispersion of palladium. Temperature-programmed reduction and temperature-programmed desorption study further demonstrated that the coating of Pd/Al 2 O 3 catalysts with titania can weaken the bond strength of Pd-O and enhance their catalytic activity towards methane combustion at lower temperature. q
Methane-to-Câ-hydrocarbon conversion activity and selectivity (or yield) of MgO and La-promoted M... more Methane-to-Câ-hydrocarbon conversion activity and selectivity (or yield) of MgO and La-promoted MgO catalysts in the oxidative coupling of methane and strong basicity of the catalysts are decreased appreciably when these catalysts are deposited on commonly used commercial low surface area porous catalyst carriers containing AlâOâ, SiOâ, SiC, or ZrOâ + HfOâ as the main components. The decrease in the strong
Journal of Chemical Technology and Biotechnology, 1998
... Vasant R. Choudhary,; Shafeek AR Mulla,; Balu S. Uphade. Article first published online: 4 MA... more ... Vasant R. Choudhary,; Shafeek AR Mulla,; Balu S. Uphade. Article first published online: 4 MAY 1999. ... Publication History. Issue published online: 4 MAY 1999; Article first published online: 4 MAY 1999; Manuscript Accepted: 13 JAN 1998; Manuscript Revised: 26 SEP 1997; ...
Catalytic steam and oxysteam reforming of methane to syngas studied involves coupling of exotherm... more Catalytic steam and oxysteam reforming of methane to syngas studied involves coupling of exothermic oxidative conversion and endothermic steam-reforming processes over Cox Ni1−x O (x = 0.0–0.5) supported on MgO precoated commercial low surface area (<0.01 m2 g−1) macroporous silica-alumina SA-5205 catalyst carrier. The influence of the Co/Ni ratio of the catalyst on its performance in steam and oxysteam reforming processes (at 800 and 850°C) was studied. For the steam reforming process, the Co/Ni ratio influences strongly on the methane and steam conversion and CO selectivity and product H2/CO ratio, particularly at lower temperature. When the Co/Ni ratio is increased, the methane and H2 O conversion and CO selectivity are decreased markedly. For the oxysteam reforming process, the influence of the Co/Ni ratio on the performance is smaller and depends on process conditions. When the Co/Ni is increased, the methane conversion passes through a maximum at the Co/Ni ratio of 0.17. The influence of the reaction temperature (800 and 850°C) and CH4/O2 and CH4/H2 O ratios on the conversion, selectivity, H2/CO product ratio, and net reaction heat (ΔHr ) was studied in the oxysteam reforming (at space velocity of 47,000 cm3·g−1·h−1) over the catalyst with an optimum Co/Ni ratio (0.17) and a higher Co/Ni ratio (1.0). The oxysteam reforming process involves coupling the exothermic oxidative conversion of methane and the endothermic methane steam reforming reactions, making the process highly energy-efficient and nonhazardous. This process can be made thermoneutral, mildly exothermic, and mildly endothermic by manipulating process conditions.
Combustion of dilute toluene and methyl ethyl ketone over Mn-doped ZrO 2 catalysts prepared using... more Combustion of dilute toluene and methyl ethyl ketone over Mn-doped ZrO 2 catalysts prepared using different precipitating agents, such as tetra-alkyl ammonium hydroxides and NH 4 OH, having Mn/Zr ratios from 0.05 to 0.67, and calcined at different temperatures has been thoroughly investigated. The Mn-doped ZrO 2 catalyst shows high toluene or methyl ethyl ketone combustion activity, particularly when its ZrO 2 is in cubic form, when its Mn/Zr ratio is close to 0.2, and when it is prepared using tetra-methyl ammonium hydroxide as a precipitating agent and calcined at 773 K.
Oxidative coupling of methane (OCM) to ethylene and ethane is a futuristic process of great pract... more Oxidative coupling of methane (OCM) to ethylene and ethane is a futuristic process of great practical importance for the effective utilization of methane/natural gas. A brief summary of the work carried out at National Chemical Laboratory (Pune) for the development of catalyst and catalytic process for OCM, particularly addressing the major issues/limitations of the OCM process and efforts made to overcome the problems is presented. This review particularly covers the development of a number of highly active/selective and stable unsupported and supported (using commercial catalyst carriers) catalysts for the OCM process and also the process of improvements/modifications to overcome most of the limitations of OCM.
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