Interaction of hydrogen chloride with alumina

The influence of temperature, pressure, and outgas conditions on the absorption of hydrogen chloride and water vapor on both alpha and gamma alumina was studied. Characterization of the adsorbents was performed using X-ray powder diffraction, scanning electron microscopy (SEM), low temperature nitrogen adsorption desorption measurements, BET nitrogen surface area measurements and electron spectroscopy for chemical analysis (ESCA). Water vapor adsorption isotherms at 30, 40, and 50 C were measured on alpha and gamma alumina after outgassing at 80, 200, and 400 C. Both outgas temperature and adsorption temperature influenced the adsorption of water vapor on the aluminas. The water vapor adsorption was completely reversible. Alpha alumina absorbed more water per unit area than gamma alumina. Differences in the adsorption capacity for water vapor of the two aluminas were explained on the basis of ideal surface models of alpha and gamma alumina. Isosteric heats of adsorption for water vapor on the aluminas were determined over a limited range of surface coverage

Role of Catalyst Support and Regioselectivity of Molecular Adsorption on a Metal Oxide Surface: NO Reduction on Cu/{\gamma}-alumina

The role of catalyst support and regioselectivity of molecular adsorption on a metal oxide surface is investigated for the NO reduction on a Cu/{\gamma}-alumina heterogeneous catalyst. For the solid surface, computational models of the {\gamma}-alumina surface are constructed based on the Step-by-Step Hydrogen Termination (SSHT) approach. Dangling bonds, which appear by cutting the crystal structure of a model, are terminated stepwise with H atoms until the model has an appropriate energy gap. The obtained SSHT models exhibit the realistic infrared (IR) and ultraviolet-visible (UV/Vis) spectra. Vibronic coupling density (VCD), as a reactivity index, is employed to elucidate the regioselectivity of the Cu adsorption on the {\gamma}-alumina and that of the NO adsorption on the Cu/{\gamma}-alumina in place of the frontier orbital theory that could not provide clear results. We discovered that the highly dispersed Cu atoms are loaded on Lewis-basic O atoms, which is known as anchoring effect, located in the tetrahedral sites of the {\gamma}-alumina surface. The role of the {\gamma}-alumina support is to raise the frontier orbital of the Cu catalyst, which in turn gives rise to the electron back-donation from the Cu/{\gamma}-alumina to NO. In addition, the penetration of the VCD distribution of the Cu/{\gamma}-alumina into the {\gamma}-alumina support indicates that the excessive reaction energies dissipate into the support after the NO adsorption and reduction. In other words, the support plays the role of a heat bath. The NO reduction on the Cu/{\gamma}-alumina proceeds even in an oxidative atmosphere because the Cu-NO bond is strongly bounded compared to the Cu-O2 bond

Catalytic oxidation of trace levels of methane in oxygen in a tubular reactor

An experimental investigation of catalytic oxidation of trace levels of methane in oxygen was conducted in a tubular reactor. Two noble metal solid catalysts were explored: a 1-percent platinum on gamma alumina and a 0.5-percent rhodium on gamma alumina. For each catalyst the activity was determined as a function of temperature, pressure, space velocity, and methane concentration. The rhodium catalyst was considerably more active than the platinum catalyst. For each catalyst mass transfer had a pronounced effect upon activity at low space velocity

Synthesis of Gamma-Alumina from Kankara Kaolin as Potential Zeolite Active Matrix

Commercial fluid catalytic cracking catalysts are manufactured using zeolites dispersed on an amorphous matrix, which is mostly alumina. Alumina is widely used as catalyst support in many heterogeneous catalytic processes owing to its high surface area, superior chemical activity and low cost. In compounded zeolite catalyst it serves as the active matrix which aids the conversion of the bulkiest molecules in the feed owing to its larger pore size than zeolite. Large specific surface area gamma-alumina (γ-Al2O3) was synthesized by hydrothermal method using Kankara kaolin as starting material. Thermal treatment of ammonium alum prepared from the filtrate of the dealuminated metakaolin was employed to obtain the alumina. Crystalline aluminum sulfate with 39 wt% Al2O3 was obtained at calcination temperature of 800°C with 3 h soaking. Gamma-alumina was produced at 850°C with 3 h soaking time, having specific surface area of 166 m2/g. The weight percent of Al2O3 content in the synthesized and commercial gamma-alumina were 85% and 89% respectively as obtained from the XRF analysis. Good comparison was also observed in the diffractogram of the synthesized and commercial gamma-alumina from the XRD analysis. The Scanning Electron Microscopy (SEM) image showed the platy hexagonal shape of the gamma-alumina.Keywords: Gamma-alumina, zeolite, kaoli

THE STUDY OF THERMAL EFFECT ON THE SURFACE PROPERTIES OF GAMMA-ALUMINA SYNTHESIED FROM KANKARA KAOLIN.

Gamma alumina is a good material for catalyst support and its surface properties is of great importance. In this study the gamma-alumina (γ-Al2O3) synthesized to be used as catalyst support for zeolite catalyst was obtained by calcination of ammonium alum an intermediate product prepared from kaolin which was sourced from Kankara, Katsina, Nigeria. The surface properties were determined using BET technique. BET specific surface area of gamma alumina produced at 825°C for soaking time of 3h was 120m2/g while at 850°C for soaking time of 4h the surface area was 140m2/g. The pore size and pore volume range from 15nm to 25nm and 0.5cm3/g to 0.8cm3/g respectively. The XRD pattern obtained at 825°C and 875°C calcination temperatures conformed to the standard pattern of gamma-alumina, having the strong peaks at Bragg angles of 67, 46, 39 and 38°. The SEM image showed clearly the plate-like structure of gamma alumina. Thus kankara kaolin is a promising material for the production of gamma alumina. http://dx.doi.org/10.4314/njt.v35i1.1

The Reactions of n-Octane on Supported Platinum Catalysts

The reaction of n-octane with hydrogen on 0.9% w/w Pt/gamma-alumina/Cl- (GHI), 0.3% w/w Pt/gamma-alumina/Cl- (EUROPT 3) and 0.3% w/w Pt - 0.3% w/w Re/gamma-alumina/Cl- (EUROPT 4) has been investigated. Catalyst activity, selectivity and stability were determined using a microcatalytic reactor under realistic reforming conditions of moderate pressure (110 psig) and high temperature (450-50

Sinter forging of zirconia toughened alumina

Sinter forging experiments have been carried out on powder compacts of zirconia toughened alumina (ZTA) Ceramics Alumina-15 wt% zirconia was prepared by a gel precipitation method and calcined at temperatures of 900 or 1100°C. Full densification of ZTA ceramics was obtained within 15 min at 1400°C and 40 MPa. A homogeneous microstructure can be observed with an alumina grain size of 0.7 mgrm and a zirconia grain size of 0.2 mgrm. Almost no textural evolution occurred in the microstructure. During sinter forging the densification behaviour of the compacts was improved by an effective shear strain, for which values of more than 100% could be obtained. As a result of the shear deformation the densification of ZTA in the agr alumina phase stage shifted to lower temperature. During pressureless sintering the gamma to agr alumina transformation temperature was dependent of the preceding calcination temperature, while during sinter forging this phase transformation was independent of calcination temperature and took place at a lower temperature

Colloidal Processing and sintering of nanosized transition aluminas

The dispersion of nanosized gamma aluminas with high specific surfaces areas (100 m2 /g) and primary particle sizes around 20 nm, using polyacrylic acid, has been investigated. The effect of pH and polymer concentration showed that the highest density green bodies were produced using high polymer concentrations (6 wt.%) and pH of 6. Interparticle potential calculations have been made and help explain the underlying dispersion mechanism at least on a qualitative level. The dispersions were then used to slip cast green bodies followed by drying and sintering. The types of gamma alumina powder have been investigated, the pure gamma alumina, doped with MgO and also with the addition of alpha alumina seeds. The high degree of agglomeration of the gamma alumina powders led to very low densities (60%) even the alpha seeded alumina reached only 85% theoretical density. Attrition milling with zirconia media improves both green density and sintered densities significantly with all powders showing sintered densities >97%. Microstructural analysis on polished and etched surfaces show, however, that the grain sizes are well above 1 Am over 50 times greater than the initial gamma alumina primary particles. A two-step sintering cycle was investigated with the Mg doped powder and average grain sizes around 580 nm were achieved

Enhanced hydrophilicity of chlorided aluminum oxide particulates

An enhancement of hydrophilicity for chlorided aluminas was demonstrated by the results obtained from gaseous H2O sorptions at 70-, 80-, and 86-percent relative humidity on alpha and gamma aluminum oxide particulates and on alpha and gamma aluminum oxide particulates with a chemisorbed surface chloride phase (produced by reactions of gaseous HCl + H2O on alumina). Continuous sorption histories for H2O on chlorided aluminas having specific surface areas that range from 7 to 227 sq m/g before chloriding indicated that initial sorption rates were directly linked to the extent of chemisorbed chlorided coverage and implied the same relationship for sorption capacities. The initial sorption rate on chlorided aluminas was found to be slower for the first exposure to H2O than for subsequent exposures (which reached equilibrated H2O coverages much faster), suggesting that slow chemical reactions between H2O and chlorided alumina may have been operative during initial exposures. Chlorided alumina particles were found to remain very hydrophilic (relative to nonchlorided analogs) for several H2O sorption/desorption cycles