Effect Of Alkaline-earth Oxides Research Articles

Base-acid tandem catalytic upgrading of coal pyrolysis volatiles: the effects of alkaline earth oxides and modified HZSM-5 zeolites

Catalytic upgrading of coal pyrolysis volatiles is a promising technology to bolster the production of value-added chemicals from coal. To optimize product distribution and mitigate catalyst deactivation, this work investigated tandem catalysts combining the upper alkaline earth oxides (CaO or MgO) with the lower modified HZSM-5 (mesopore creation and Ga loading). The pre-cracking of volatiles over CaO or MgO lowered the average molecule size of tar components. The diffusion properties and aromatization of these pre-cracking-derived intermediates were improved, facilitating the secondary upgrading over HZSM-5-based catalysts, promoting the formation of aromatics. The experimental results showed that tandem CaO-HZSM-5 catalysts presented better synergy to improve the tar components as compared to MgO-HZSM-5, considering the formation of aromatics in tar. In this context, the mesopore and metal Ga were introduced into HZSM-5 to further upgrade the tar quality. The mesoporous structure for HZSM-5-meso and Ga/HZSM-5-meso promoted the conversion of aliphatic hydrocarbons into aromatics. Simultaneous introduction of mesopores and Ga synergistically increased the aromatic content in tar to 41.6% and reduced the carbon deposition to 0.88wt.%. In summary, this work elucidated the mechanism of tandem CaO-modified HZSM-5 catalysis for the upgrading of volatiles from coal pyrolysis.

Effect of Alkaline earth oxides on the ionic conductivity of Boro-Tellurite glasses for solid state ion batteries

The complex impedance spectroscopy studies (electrical impedance, a.c. conductivity, dielectric constant, loss tangent) of the boro-tellurite glasses were measured as a function of the alkaline earth oxide content at broad range of frequencies and temperatures. Three series of boro-tellurite glasses containing BaO/SrO viz. BaO-TeO2-TiO2-B2O3 (BTTB), BaO-TeO2-B2O3 (BTB) and SrO-TeO2-TiO2-B2O3 (STTB) were prepared by the melt quenching method. The prepared glasses were characterized by XRD, DSC, density, FTIR and complex impedance spectroscopy experimental techniques. The XRD spectra exhibited no characteristic sharp peaks indicating the amorphous nature of the prepared glass samples. The glass transition temperature (Tg) values were evaluated from the DSC thermograms. The density values were found to increase with BaO content while they decreased with SrO content. This variation was attributed to the different density values of BaO and SrO. FTIR spectra revelated the presence of different structural units like BO3 and BO4. Impedance studies demonstrated that the replacement of TeO2 by the BaO content enhanced the ionic conductivity. The impedance plots of BTTB, BTB and STTB glasses exhibited nearlys semicircles. The bulk resistance (Rb) was calculated from the impedance plots. It was observed that the Rb values decrease with increasing BaO in BTTB and BTB glasses, while it increased with SrO in STTB glasses which may be attributed to the variation of mobile charge carriers. The Rb values vary as BTB > BTTB > STTB. The capacitance calculated from the impedance plots increased with increasing BaO mol% and decreasing SrO mol%. The capacitance also increased with increasing temperature. The power law exponent (k) values decrease with increasing temperature. Therefore, the ac conduction mechanism may follow correlated barrier hopping model. The real part of dielectric constant has high values at low frequencies, which decreased rapidly with surge of frequency. At high frequencies the contribution of charge accumulation is minimum resulting in constant

Effect of alkaline earth oxides on nickel catalysts supported over γ-alumina for butanol steam reforming: Coke formation and deactivation process

Nickel catalysts were synthesized by the wet impregnation of three different supports: γ-Al2O3 and alumina promoted with either 10 wt % of MgO or 10 wt% of CaO. The catalysts were evaluated in butanol steam reforming at 500 °C, atmospheric pressure, GHSV of 500,000 h−1 and 10% v/v butanol in the feed. Both promoters decreased catalyst acidity and increased basicity. The catalyst promoted with MgO exhibited the lowest acidity (1.1 μmolNH3 m−2), whereas that promoted with CaO, the highest basicity (870.7 μmolCO2 m−2). The promotion with MgO led to the highest hydrogen yield (66%) and stability, associated with its highest nickel dispersion (3.4%), lowest acidity and lowest coke formation normalized by carbon converted (3.0 mmol L mol−1). The catalyst promoted with CaO presented the most severe deactivation, associated with its lowest dispersion (1.0%) and the highest amount of encapsulated coke (3.5 mmol L mol−1).

Effects of alkaline earth oxides on the densification and microwave properties of low-temperature fired BaO–Al2O3–SiO2 glass–ceramic/Al2O3 composites

The effects of alkaline-earth oxides (SrO, CaO, MgO) on the densification and microwave properties of low-temperature fired BaO–Al2O3–SiO2 (BAS) glass–ceramic/Al2O3 composites have been investigated. By adding alkaline-earth oxides, the softening and crystallization behaviors of BAS-based glass–ceramics, which determine the densification of composites, are sequentially weakened in the order of BAS, SrO–BaO–Al2O3–SiO2 (SBAS), CaO–BaO–Al2O3–SiO2 (CBAS) and MgO–BaO–Al2O3–SiO2 (MBAS). It is also found in the above BAS-based glass–ceramics that the addition of alkaline-earth oxides plays a more profound role on crystallization behavior than on softening behavior, leading to the expansion of the interval between crystallization and softening temperatures (i.e., densification temperature range) to different degrees depending on the type of oxides added. As a result, the microstructures of oxides-modified glass–ceramic/Al2O3 composites (SBAS/Al2O3, CBAS/Al2O3, MBAS/Al2O3) are much denser than those of BAS/Al2O3. The properties of such composites are determined by the interplay among density of microstructure, amount and relative ratio of crystalline and residual glass phases related to the crystallization behavior and interfacial reaction. Detailed analyses suggest that CBAS/Al2O3 achieves optimal properties among all the four composites. Specifically, for CBAS/Al2O3 the dielectric constant, dielectric loss, bending strength and CTE value are 5.81 ± 0.12 (at ~ 10 GHz), (2.04 ± 0.12) × 10−3 (at ~ 10 GHz), 155 ± 7 MPa and 6.58 ± 0.11 ppm/°C, respectively. Our findings may provide a new avenue to design LTCC substrate materials as feasible candidates for microwave devices.

Effect of alkaline earth oxides on the physical and spectroscopic properties of Dy3+- doped Li2O-B2O3 glasses for white emitting material application

Li2O–MO-B2O3:0.5Dy2O3 glasses mixed with four different alkaline earth modifier oxides MgO, CaO, SrO and BaO were synthesized by melt quench technique. Their physical properties like density, molar volume and refractive index were measured at room temperature and the effect of alkaline earth modifier oxides were studied. Also, optical absorption and photoluminescence spectra of these glasses have been acquired at room temperature. The Judd–Ofelt theory was effectively used to characterize these spectra and spectral intensities (ƒcal), Judd–Ofelt intensity parameters (Ω2, Ω4 and Ω6) and certain radiative properties have been determined. Radiative life-times (τR), branching ratios (βcal), and emission cross-sections (σp) and optical gain parameters (σp × τR) were calculated from the Judd–Ofelt intensity parameters and the variation in these parameters with the variation of glass matrix are discussed. Yellow/Blue (Y/B) ratio and chromacity color coordinates (x,y) are calculated from the emission spectra which indicates the white light generation from all the investigated samples. The correlated color temperature (CCT) for the studied glasses is found to be 4418 K. The fluorescence decay time (τexp) of the 4F9/2 level of Dy3+ has been measured from the decay profiles and compared with calculated lifetimes (τcal). Among all the studied glass matrices, the glass containing BaO exhibits high value of branching ratio, large emission cross-section and high optical gain parameter for 6F9/2 → 6H13 at 575 nm. The results indicates the suitability of all the studied glasses for laser action and white light generation.

Effects of alkaline-earth oxides on the performance of a CuO–ZrO2catalyst for methanol synthesis via CO2hydrogenation

The incorporation of alkaline-earth oxides into CuO–ZrO2catalyst affects the Cu surface area, the reducibility of CuO, the surface basicity and further the CO2conversion and methanol selectivity.

Effects of alkaline earth oxides on precipitation behavior of metallic iron under CO atmosphere

In gaseous reduction of iron ore fines, alkaline earth oxides have profound effects on the precipitation behavior of fresh metallic iron on the particle surface. In this work, in situ observation was performed to reveal the influence of alkaline earth oxides on the precipitation morphology and micro-structure variation of fresh metallic iron from microscopic level by simulation of the gas-solid reaction condition on the surface of ore particles. Experimental results indicate that doping MgO in the particle surface can inhibit the reduction of iron oxide and however doping CaO, SrO and BaO promote; all alkaline earth oxides tested in this study can change the precipitation morphology of fresh metallic iron; minimum doping mole fraction of one oxide to inhibit iron whiskers growth (NAO) is related to its cation radius \(\left( {r_{A^{2 + } } } \right)\) and its extranuclear electronic layers \(\left( {n_{A^{2 + } } } \right)\), which can be expressed as \(N_{AO} = 1.3 \times 10^{ - 5} r_{A^{2 + } }^2 \sqrt {n_{A^{2 + } } }\).

Effect of alkaline earth oxides on ceramization of LaF 3 in aluminosilicate glass: 19F MAS-NMR study

Local environment of fluorine atoms in the lanthanum oxyfluoride aluminosilicate glasses and glass-ceramics modified by alkaline earth oxides, i.e. MgO, CaO and BaO, was studied by solid state 19F MAS-NMR spectroscopy. The effect of the type and concentration of the modifier on the formation of crystalline LaF 3 phase was determined, as a function of heat treatment conditions. In all series of glasses studied, the F–Me(n), but no Na–F species were observed. The presence of F–La,Ba(n) units, in which fluorine is coordinated both by lanthanum and barium, was detected in the Ba-glass. Supplementary XRD analysis of this series confirmed that an increase of barium contents leads to the formation of Ba 0.3La 0.7O 0.7F 1.3, instead of pure LaF 3 only.

Highly Efficient Ru-Ba/AC Catalyst Promoted by Magnesium for Ammonia Synthesis

The effect of alkaline-earth oxides as promoters on Ru/AC (AC = activated carbon) catalysts was explored. Alkaline-earth metal oxides can reduce the agglomeration of ruthenium particles at high temperatures, which increases the amount of available ruthenium. The influence of the Mg promoter on the distribution and activity of the Ru/AC catalyst were investigated by CO chemisorption, X-ray diffraction, and energy dispersive spectrometry and by an activity test for ammonia synthesis. The results show that a specific quantity of magnesium significantly promotes the uniform distribution of Ba and Ru on the surface of AC, which enhances catalytic activity. The introduction of Mg significantly improved the size of the Ru particles and increased the Ru surface area. The distribution and interaction were improved greatly for the Ba promoter and the Ru precursor on the surface of the AC because of the addition of the Mg promoter. The introduction of magnesium to Ru-Ba-K/AC significantly improved the utilization ratio of the noble metals and the performance-price ratio. ：通过 X 射线衍射、CO 化学吸附、X 射线光电子能谱和氨合成活性测试等手段, 研究了 Mg 助剂对 Ru/AC 催化剂组分分布和活性的影响. 结果显示, 适量 Mg 的添加有利于 Ba 和金属 Ru 粒子在活性炭表面的均匀分布, 从而提高了催化剂活性. A highly efficient Ru-Ba/AC catalyst promoted by magnesium gave a high dispersion and a good interaction was evident between Ru and Ba during ammonia synthesis.

Catalytic effect of alkaline earth oxides on carbothermic formation of hexagonal boron nitride

Effect of MgO, CaO and BaO on carbothermic formation of hexagonal boron nitride (h-BN) was investigated. B 2O 3–C mixtures containing alkaline earth oxide additives were reacted at 1500 °C for 30–120 min in nitrogen atmosphere. Formed phases in the reaction products were determined by powder-XRD analyses, and amounts of the constituents were determined by chemical analyses. Particle size and morphology of the formed h-BN powders were examined by FESEM and particle size distributions were determined by particle size analyzer. Addition of alkaline earth oxides was found to increase the amount and grain size of h-BN significantly and to decrease the amount of B 4C formed in the system. Investigated alkaline earth oxides presented similar catalytic effects according to chemical analyses and FESEM observations. While the average particle size of h-BN powder obtained from plain mixture was 149 nm, those obtained from MgO, CaO and BaO containing mixtures were 297, 367 and 429 nm, respectively.

Comparative investigation on the effect of alkaline earth oxides on the intensity of absorption bands due to Cu2+, Mn3+ and Cr3+ ions in ternary silicate glasses

Absorption characteristics of Cu2+, Mn3+ and Cr3+ ions in ternary silicate (20Na2O·10RO·70SiO2, where R=Ca, Sr, Ba) glasses were investigated. The intensities of absorption bands due to Cu2+ ion was found to increase with increasing ionic radii of the alkaline earth ions whereas it was found to decrease in case of Mn3+ and Cr3+ ions with increasing ionic radii of the alkaline earth ions. The results were discussed in the light of relation between linear extinction coefficients of these ions and coulombic force of alkaline earth ions. The change in intensities of Cu2+, Mn3+ and Cr3+ ion is attributed due to change in silicate glass compositions.

Effect of alkaline-earth oxides on phase formation and morphology development of mullite ceramics

The effect of alkaline-earth oxides, including MgO, CaO, SrO and BaO, on the phase formation and morphology development of mullite (3Al 2O 3·2SiO 2) ceramics from oxide mixtures activated by a high-energy ball milling process, were investigated. Different alkaline-earth oxides demonstrated different influences on the mullitization behavior and morphology/microstructure development of the mullite ceramics. Mullitization temperature increased as the additives were from MgO to BaO. Well developed mullite whiskers were formed in the MgO doped group, while grains with normal shapes were observed in the cases of CaO, SrO and BaO. The dependence of both mullite formation temperature and morphology development on the kinds of alkaline-earth oxides were explained in terms of the mullitization mechanism of dissolution–precipitation.

Promoting effects of alkaline earth oxides on the vapor phase carbonylation of ethene over cluster-derived cobalt catalysts

Alkaline earth oxide modified Co/SiO 2 catalysts derived from a cobalt carbonyl cluster [Co 2(CO) 8] exhibit high selectivities for vapor phase carbonylation of ethene to produce propanal, n-propanol, propanoic acid, and aldol condensates of propanol under the reaction conditions of 1.1 MPa of a gas-mixture of Ar:C 2H 4:CO:H 2=1:3:3:3 at 423–503 K. Alkaline earth oxides notably promote the formation of propanoic acid and aldol condensates. The carbonylation selectivity of cobalt-alkaline earth oxide/SiO 2 catalysts was increased in the following order: alkaline earth oxide=none<Mg<Ba≈Sr≈Ca.

Effect of alkaline-earth oxides on crystallization of zirconium compounds in low-melting glazes

Effect of alkaline-earth oxides on crystallization of zirconium compounds in low-melting glazes