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An effective and versatile synthetic approach is presented to prepare highly selective and stable bimetallic PdNi catalyst for selective hydrogenation of acetylene. NiMgAl-layered double hydroxide (LDH) was synthesized by separate nucleation and aging steps, followed by the introduction of PdCl42− to obtain the catalyst precursor. The positive charge of NiMgAl-LDH layer offers an opportunity to realize uniform dispersion of PdCl42−, which facilitates the formation of bimetallic PdNi nanoparticles. Upon thermal reduction of PdCl42−/NiMgAl-LDH precursor, highly dispersed bimetallic PdNi/MgAl-MMO catalyst was obtained. As comparison, MMO-supported PdNi catalyst was also prepared by the co-impregnation and sol-immobilization method. The catalyst derived from LDH precursor exhibited much higher activity and selectivity toward ethene than that prepared by other two methods, which could be attributed to smaller metal particle size and stronger interaction between two metals. Furthermore, because of preferable structure stability, this catalyst also possessed higher stability of activity. Preferable structure stability of the catalyst could be due to the net trap effect of MgAl-MMO microcrystals stemming from LDH precursor, which provided fixed positions for the PdNi nanoparticles during the reaction.

Pseudoboehmite was synthesized using the separate nucleation and aging steps (SNAS) method for the first time. An alumina support (Al2O3(PB)) was then prepared by extrusion method using the synthesized pseudoboehmite as precursor. Compared with spherical alumina (Al2O3(OD)) prepared by the conventional oil-drop method, Al2O3(PB) exhibits higher surface area, more regular pore structure and narrower pore size distribution. Al2O3(PB) and Al2O3(OD) were used as supports to prepare Pd catalysts. The catalytic performance of the two Pd catalysts was investigated in the catalytic hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone, a key step in the anthraquinone process for the manufacture of hydrogen peroxide. Compared with Pd/Al2O3(OD) catalyst, Pd/Al2O3(PB) catalyst showed higher Pd dispersion and thinner Pd penetration depth which resulted in more catalytically active site and easier diffusion of the reactants, and consequently Pd/Al2O3(PB) catalyst exhibited higher anthraquinone hydrogenation activity and better selectivity.

A Pd catalyst supported on a layered double hydroxide (LDH or hydrotalcite-like material) has been synthesized in a one step reaction using a precipitation–reduction method in which hydrolysis of hexamethylenetetramine was used to both precipitate the LDH by virtue of the resulting increase in pH and provide formaldehyde which reduces the Pd2+ precursor to Pd0. The resulting Pd nanoparticles were mostly tetrahedral in shape, and were highly dispersed on the surface of the LDH. After introducing a capping agent during the synthesis, the morphology of the Pd particles changed to truncated octahedral, although a similar high degree of dispersion was obtained. Compared with a conventional impregnated catalyst composed of pseudo-spherical Pd particles, catalysts prepared by the new method showed both higher activity and selectivity in the hydrogenation of acetylene. The enhanced activity is due to the specific morphology of the Pd particles, which results in their higher dispersion, while the higher selectivity is attributed to the Pd–C phase formed in the catalyst during the reaction. Furthermore, compared with the truncated octahedral Pd particles enclosed by (1 1 1) and (1 0 0) facets, the tetrahedral particles with only (1 1 1) facets exposed showed higher ethylene selectivity, suggesting that the Pd (1 1 1) facet is the preferred facet in the selective hydrogenation of acetylene to ethylene.

MgAl–CO3-layered double hydroxides (MgAl-LDHs) have been synthesized on the surface of spherical γ-Al2O3 by an in situ synthesis technique using urea as a precipitant. After calcination, LDH crystallites are transformed into complex metal oxides (LDO) with high homogeneity and MgAl-LDO/γ-Al2O3 solid base catalysts containing different LDO content were obtained. X-ray diffraction, scanning electron microscopy, and surface area measurements using the Brunauer–Emmett–Teller method indicated that the MgAl-LDO/γ-Al2O3 catalysts possess high specific surface area and rich mesoporous structure. The MgAl-LDO/γ-Al2O3 catalysts were used to regenerate anthraquinone degradation products formed in the anthraquinone process for the manufacture of hydrogen peroxide. The efficiency of regeneration of the anthraquinone degradation products was found to increase with increasing LDO loading in the catalysts. Compared with commercial catalysts of NaOH/γ-Al2O3 and MgO/γ-Al2O3 prepared by the impregnation method, MgAl-LDO/γ-Al2O3 catalysts exhibited not only higher activity but also longer life.

Spherical Al2O3 and SiO2–Al2O3 supports with different silica contents have been synthesized by the oil column method. After impregnation with Na2PdCl4 solution and subsequent calcination, PdO/Al2O3 and PdO/SiO2–Al2O3 catalyst precursors were obtained. X-ray powder diffraction and low temperature N2 adsorption–desorption measurements showed that the addition of silica increased the thermal stability, surface acidity, specific surface area and total pore volume of the spherical alumina. Temperature programmed reduction and H2–O2 titration indicated that Pd supported on the SiO2–Al2O3 spheres possessed higher dispersion and smaller particle size than that supported on pristine spherical Al2O3. Catalytic hydrogenation of ethylanthraquinone using molecular hydrogen was studied over the reduced Pd/Al2O3 and Pd/SiO2–Al2O3 catalysts with different silica contents. Under identical reaction conditions, the reaction activity and stability increased with increasing silica content.

Layered double hydroxide (LDH) precursors with the compositions Mg 2+ –Fe 2+ –Fe 3+ –CO 3 2− –LDHs, Ni 2+ –Fe 2+ –Fe 3+ –CO 3 2− –LDHs and Co 2+ –Fe 2+ –Fe 3+ –CO 3 2− –LDHs have been synthesized by a method involving separate nucleation and aging steps (SNAS). After calcination at 900 °C, MgFe 2 O 4 , NiFe 2 O 4 and CoFe 2 O 4 spinel ferrites were obtained. Vibrating sample magnetization (VSM) measurements indicate that NiFe 2 O 4 has the best combination of soft magnetic properties with high specific saturation magnetization, low remanence and low coercivity. Silica was coated onto the surface of the NiFe 2 O 4 spinel ferrite particles, and the coated particles were used as magnetic cores for the preparation of porous magnetic micro-spherical alumina particles (NiFe 2 O 4 –SiO 2 –Al 2 O 3 ) by the oil column method. Scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and low temperature nitrogen adsorption measurements indicate that the sphericity, magnetic properties and pore structure of NiFe 2 O 4 –SiO 2 –Al 2 O 3 are suitable for practical applications as a catalyst or catalyst support.