Direct synthesis and catalytic performance of ultralarge pore GaSBA-15 mesoporous molecular sieves with high gallium content

Mesoporous GaSBA-15 molecular sieves with different n_Si/n_Ga ratios have been directly synthesized using Pluronic 123 triblock polymer as a structure-directing agent by pH-adjusting method. The mesoporous materials have been characterized using ICP-AES, XRD, N₂ adsorption, ⁷¹Ga-MAS NMR, SEM and TEM. ICP-AES studies show a high amount of gallium incorporation on the silica pore walls. The structural and textural properties of calcined GaSBA-15 are characterized by XRD and N₂ adsorption. ⁷¹Ga MAS NMR results demonstrate that a high amount of tetrahedral-gallium could be substituted for Si in the framework of SBA-15. TEM and FE-SEM images show the uniform pore diameter and rope-like hexagonal mesoporous structure of GaSBA-15. These GaSBA-15 materials have been used as catalysts for vapour-phase t-butylation of 1,2-dihydroxybenzene (DHB) for selective synthesis of 4-t-butylcatechol (4-TBC) under different reaction conditions. GaSBA-15(10) gave the highest 93.2% conversion of DHB and 95.7% selectivity of 4-TBC as compared with other GaSBA-15 catalysts.     

Chemical looping glycerol reforming for hydrogen production by Ni@ZrO2 nanocomposite oxygen carriers

The research describes the synthesis of nanocomposite Ni@ZrO₂ oxygen carriers (OCs) and lanthanide doping effect on maintaining the platelet-structure of the nanocomposite OCs. The prepared OCs were tested in chemical looping reforming of glycerol (CLR) process and sorption enhanced chemical looping reforming of glycerol (SE-CLR) process. A series of characterization techniques including N₂ adsorption-desorption, X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), high resolution transmission electron microscopy (HRTEM), H₂ temperature-programmed reduction (H₂-TPR), H₂ pulse chemisorption and O₂ temperature-programmed desorption (O₂-TPD) were used to investigate the physical properties of the fresh and used OCs. The results show that the platelet-stack structure of nanocomposite OCs could significantly improve the metal support interaction (MSI), thus enhancing the sintering resistance. The effect of lanthanide promotion on maintaining this platelet-stack structure increased with the lanthanide radius, namely, La³⁺ > Ce³⁺ > Pr³⁺ > Yb³⁺. Additionally, the oxygen mobility was also enhanced because of the coordination of oxygen transfer channel size by doping small radius lanthanide ions. The CeNi@ZrO₂ showed a moderate ‘dead time’ of 220 s, a high H₂ selectivity of 94% and a nearly complete glycerol conversion throughout a 50-cycle CLR test. In a 50-cycle SE-CLR stability test, the CeNi@ZrO₂CaO showed high H₂ purity of 96.3%, and an average CaCO₃ decomposition percentage of 53% without external heating was achieved.     

Oxidative decomposition of naphthalene by supported metal catalysts

A fixed-bed reactor was utilized to investigate the activities of six metal catalysts (1% Pt, 1% Pd, 1% Ru, 5% Co, 5% Mo and 5% W on γ-Al₂O₃ support) in decomposing naphthalene, based on the production of carbon dioxide and the disappearance of naphthalene. The Pt and Pd catalysts were found to exhibit higher naphthalene oxidizing activity than other catalysts tested. The Co catalysts, whose activity is similar to that of the Ru catalysts, are promising for naphthalene oxidation. The kinetic results of naphthalene oxidation over 1% Pt/γ-Al₂O₃ catalysts are reported for the first time. A first-order reaction with respect to P_naphthalene was found, while the reaction order with respect to P_O2 decreased with increasing reaction temperatures. A Langmuir–Hinshelwood model was used to describe the observed kinetic behavior. Oxygen adsorption dominates at higher reaction temperatures (>140 °C), and consequently the oxidation of naphthalene over the Pt catalysts appeared to be insensitive to P_O2.     

La0.6Sr0.4Co0.8Ni0.2O3−δ hollow fiber membrane reactor: Integrated oxygen separation – CO2 reforming of methane reaction for hydrogen production

An integrated reactor system which combines oxygen permeable La_0.6Sr_0.4Co_0.8Ni_0.2O_3−δ (LSCN) perovskite ceramic hollow fiber membrane with Ni based catalyst has been successfully developed to produce hydrogen through oxy-CO₂ reforming of methane (OCRM). Dense La_0.6Sr_0.4Co_0.8Ni_0.2O_3−δ hollow fiber membrane was prepared using phase inversion-sintering method. OCRM reaction was tested from 650 °C to 800 °C with a quartz reactor packed with 0.5 g Ni/Al₂O₃ catalyst around the LSCN hollow fiber membrane. CH₄ and CO₂ were used as reactants and air as the oxygen source was fed through the bore side of the hollow fiber membrane. In order to gauge the effectiveness of this membrane reactor system, air flow was closed at 800 °C and dry reforming of methane (DRM) was tested for comparison. The results show that the oxygen fluxes of LSCN membrane swept by helium are nearly 3 times less than those swept by OCRM reactants. With increasing temperature and oxygen supply, methane conversion in the OCRM reactor reaches 100%, but CO₂ conversion decreases from 87% to 72% due to the competition reaction with POM. CO selectivity is as high as nearly 100% at reaction temperatures of 700 °C–800 °C while H₂ selectivity reaches a maximum of 88% at 700 °C. At 800 °C, when air supply was closed and DRM was conducted for comparison, CO selectivity decreased to 91%, resulting in carbon deposition which was around 4 times more than those obtained under OCRM reaction and H₂/CO ratio decreased from 0.93 to 0.74, showing better carbon resistance and higher H₂ selectivity of the Ni-based catalyst over the integrated oxygen separation-OCRM reaction across the LSCN hollow fiber membrane reactor.     

Adsorption behaviors and mechanisms of porous hypercrosslinked polymers with adjustable functional groups toward doxycycline hydrochloride from water

Imino hypercrosslinked polymers (NH-HCPs), amino hypercrosslinked polymers (NH₂-HCPs), and carboxyl hypercrosslinked polymers (COOH-HCPs) were synthesized through cross-linking and Friedel-Crafts reactions to serve as highly efficient adsorbents for doxycycline hydrochloride (DOX) in water. These polymers, NH-HCPs, NH₂-HCPs, and COOH-HCPs, exhibited specific surface areas measuring 450, 267.576, and 94.39 m²/g, respectively. The adsorption kinetics of DOX onto these polymers were consistent with the pseudo-second-order model, while the adsorption isotherms followed the Langmuir model (NH-HCPs) and Freundlich model (NH₂-HCPs and COOH-HCPs), respectively. The maximum DOX adsorption capacities for NH-HCPs, NH₂-HCPs, and COOH-HCPs were 166.82, 132.43, and 72.07 mg/g, respectively. Simulation results indicated that COOH-HCPs exhibited the strongest adsorption capability due to a substantial presence of oxygen and nitrogen groups on its surface, enabling the formation of hydrogen bonds with DOX. However, its actual adsorption capacity was the lowest among the polymers, indicating that structural adjustments played a more significant role in improving adsorption performance compared to functional adjustments. Adsorption experiments conducted with NH-HCPs and NH₂-HCPs further supported this hypothesis. The primary DOX adsorption mechanism of NH-HCPs, NH₂-HCPs, and COOH-HCPs involved the H-bonding of oxygen and nitrogen functional groups, along with other mechanisms such as π-π conjugated effects, pore-filling effects, electrostatic interactions, and acid–base interactions. Overall, this study demonstrates the effectiveness of NH-HCPs, NH₂-HCPs, and COOH-HCPs in DOX removal from water, highlighting the significant influence of structural adjustments on adsorption performance.     

CO2 dry-reforming of methane over La0.8Sr0.2Ni0.8M0.2O3 perovskite (M = Bi,Co, Cr,Cu, Fe): Roles of lattice oxygen on C–H activation and carbon suppression

La_0.8Sr_0.2Ni_0.8M_0.2O₃ (LSNMO) (where M = Bi, Co, Cr, Cu and Fe) perovskite catalyst precursors have been successfully developed for CO₂ dry-reforming of methane (DRM). Among all the catalysts, Cu-substituted Ni catalyst precursor showed the highest initial catalytic activity due to the highest amount of accessible Ni and the presence of mobile lattice oxygen species which can activate C–H bond, resulting in a significant improvement of catalytic activity even at the initial stage of reaction. However, these Ni particles can agglomerate to form bigger Ni particle size, thereby causing lower catalytic stability. As compared to Cu-substituted Ni catalyst, Fe-substituted Ni catalyst has low initial activity due to the lower reducibility of Ni–Fe and the less mobility of lattice oxygen species. However, Fe-substituted Ni catalyst showed the highest catalytic stability due to: (1) strong metal–support interaction which hinders thermal agglomeration of the Ni particles; and (2) the presence of the abundant lattice oxygen species which are not very active for C–H bond activation but active to react with CO₂ to form La₂O₂CO₃, hence minimizing carbon formation by reacting with surface carbon to form CO.     

Promotional effect of alkaline earth over Ni-La2O3 catalyst for CO2 reforming of CH4: Role of surface oxygen species on H2 production and carbon suppression

Alkaline earth elements (Mg, Ca and Sr) on Ni-La₂O₃ catalyst have been investigated as promoters for syngas production from dry CO₂ reforming of methane (DRM). The catalysis results of DRM performance at 600 °C show that the Sr-doped Ni-La₂O₃ catalyst not only yields the highest CH₄ and CO₂ conversions (∼78% and ∼60%) and highest H₂ production (∼42% by vol.) but also has the lowest carbon deposition over the catalyst surface. The XPS, O₂-TPD, H₂-TPR and FTIR results show that the excellent performance over the Sr-doped Ni-La₂O₃ catalyst is attributed to the presence of a high amount of lattice oxygen surface species which promotes C-H activation in DRM reaction, resulting in high H₂ production. Moreover, these surface oxygen species on the Ni-SDL catalyst can adsorb CO₂ molecules to form bidentate carbonate species, which can then react with the surface carbon species formed during DRM, resulting in higher CO₂ conversion and lower carbon formation.     

Enhanced performance and selectivity of CO2 methanation over g-C3N4 assisted synthesis of NiCeO2 catalyst: Kinetics and DRIFTS studies

The hydrogenation of CO₂ on CeNi catalyst modified with g-C₃N₄ (CeNiCN) as a sacrificial and protective template was studied by in-situ DRIFTS and Kinetics experiments to investigate the influence of modification on the catalytic activity and selectivity to gain mechanistic insight. After modification, the catalyst showed higher catalytic activity and selectivity. H₂-TPR, CO₂-TPD, TEM and XPS confirmed that this modification could enhance the interaction of nickel and ceria and decrease the particle size of nickel, which is in favor of the dissociation of H₂ and adsorption of CO₂. The in-situ DRIFTS experiments demonstrated that CO₂ is adsorbed on ceria sites, forming carboxylate (CO₂^δ?), unidentate carbonate and bicarbonates, which, in turn, react with adsorbed and dissociated H on Ni to produce formate species. Furthermore, adsorbed methoxy species were observed, which are recognized to be intermediates in the methanation process. In-situ transient DRIFTS confirm that the adsorbed CO is not a reaction intermediate, but a by-product, which originates from the decomposition of weak-binding formate species on Ce³⁺ sites. The unmodified catalyst has more weak-binding formate species, which are more inclined to decompose into CO accounting for the low selectivity. Furthermore, the adsorbed CO on Ce³⁺ sites cannot react with the adsorbed hydrogen to produce methane. Kinetics studies are consistent with a Langmuir-Hinshelwood type mechanism in which the formation of bicarbonate is the rate-determining step (RDS).     

Steam reforming of toluene as a biomass tar model compound over CeO2 promoted Ni/CaO–Al2O3 catalytic systems

Steam reforming of toluene as a biomass tar model compound was performed over Ni supported CaO–Al₂O₃ (Ca–Al) and CeO₂ promoted CaO–Al₂O₃ (Ca–Al–Ce) catalysts to explore promotional effect of CeO₂ on Ca–Al support. Among all the catalysts tested, Ni/Ca–Al–Ce(0.2) catalyst gave superior catalytic performance over other catalysts. The basic strength of catalytic supports measured by CO₂ TPD and Hammett indicator methods indicates Ca–Al–Ce(0.2) support has higher surface basicity and base strength compared to Ca–Al and other Ca–Al–Ce(x) supports. Furthermore, CO pulse chemisorption results showed that Ni/Ca–Al–Ce(0.2) catalyst has a higher amount of surface metallic nickel compared to other Ni/Ca–Al–Ce catalysts. TPR analysis reveals that the redox property of CeO₂ can enhance the reducibility of supported nickel species, which is further confirmed using XPS analysis, where addition of CeO₂ enhanced the interaction of Ni species with Ce by reducing the interaction of Ni species with the Al support, resulting in the formation of Ni° rich surface. However, formation of bulk NiO species was also observed for the catalyst having higher amount of CeO_2. TGA analysis on spent catalysts reveals that all CeO₂-containing catalysts generally result in lower carbon formation rates as compared to Ni/Ca–Al catalyst.     

Dendritic SBA-15 supported Wilkinson's catalyst for hydroformylation of styrene

After PAMAM (polyamidoamine) dendrimers have been successfully grown in SBA-15 mesoporous materials, Wilkinson's catalyst (RhCl(PPh₃)₃) precursor has been tethered on these dendritic supports to produce heterogeneous catalysts for hydroformylation reaction of styrene. SBA-15 has been functionalized by two methods. In the passivation method, the silanols outside the SBA-15 pores have been passivated to preclude the rhodium precursor to be tethered outside the channels. The rhodium catalysts supported in the pore channels of this passivated SBA-15 show positive dendritic effects in enhancing the catalytic activity, regio-selectivity and stability of the catalyst by minimizing the leaching of the rhodium complex catalyst from the catalyst support to the liquid-phase media.