Au–Pd NPs immobilised on nanostructured ceria and titania: impact of support morphology on the catalytic activity for selective oxidation

Abstract

Bimetallic Au-Pd nanoparticles supported on different ceria and titania nanostructures have been prepared by sol-immobilisation, and evaluated in the solvent-less selective oxidation of benzyl alcohol. The catalysts were characterised by TEM, STEM, XRD, XPS, ICP-AES, and nitrogen adsorption-desorption measurements.The activity of the catalysts was found to be strongly related to the morphology, structure and physiochemical properties of the supports. Au-Pd/ceria nanorods exhibited remarkably high catalytic activity (TOF > 35 900 h −1 ), and was found to be considerably more active than Au-Pd/titanate nanotubes, and Au-Pd catalysts supported on conventional ceria and titania nanopowders. The outstanding catalytic performance of Au-Pd/ceria nanorods is attributed to the unique surface chemistry of ceria nanorods, and the ability of catalyst preparation method (i.e. sol-immobilisation) to control the metal particle size and the bimetallic alloy formation. The presence of surface defects and high concentration of oxygen vacancies and Ce 3+ in ceria nanorods is likely responsible for the stabilisation of Au-Pd NPs during sol-immobilisation, which led to a very small mean particle size (2.1 nm) corresponding to a dispersion of approximately 52%, and a high surface metal concentration.

Investigations of supported Au-Pd nanoparticles on synthesized CeO2 with different morphologies and application in solvent-free benzyl alcohol oxidation

“…Based on the observed Pd and Au elements on the cata-lysts by using XPS, the molar ratios of Au/Pd were calculated and ranked by ACP > ACR > ACC. These values based on the XPS characterization were found lower than the nominal Au/Pd values, which suggests the enrichment of Pd species on CeO2 surface, the si-milar phenomenon was also reported by David et al, which could be assigned to the variation in XPS analysis depths between Pd and Au [15].…”

“…Liu et al synthesized CeO2 rod under the protection of N2 followed by in-situ load of Au and Pd nanoparticles applying surface redox mechanism between CeO2 and noble metal to produce AuPd/CeO2 rod catalyst, which showed high benzyl alcohol conversion and benzaldehyde selectivity [14]. David et al also prepared Au-Pd/CeO2 nanorod catalyst with sol-immobilization method using NaBH4 as a reducing agent, which exhibited high catalytic activity in the same reaction under solvent-free condition [15]. In addition, Au-Pd supported on ceria-zirconia mixed oxide was also applied for the benzyl alcohol oxidation, a synergistic effect existed between Au and Pd during the reaction [16,17].…”

Solvent-Free Catalytic Oxidation of Benzyl Alcohol over Au-Pd Bimetal Deposited on TiO2: Comparison of Rutile, Brookite, and Anatase

“…Nevertheless, the higher ratios of Pd 2+ on the ATR and ATB indicated that the TiO 2 carrier also played an essential role in promoting the formation of Pd 2+ , which could supply oxygen to assist the production of Pd 2+ . The existence of Pd 2+ species further demonstrates that some Pd cannot alloy with Au; this phenomenon has been reported in the similar Au-Pd/CeO 2 catalyst [18]. The XPS spectra of O1s on the ATA, ATB, and ATR catalysts are exhibited in Fig.…”

Supported Gold Nanoparticles as Catalysts for the Oxidation of Alcohols and Alkanes

“…The use of microwave is regarded as much more effective, when compared with conventional heating, usually with similar yields achieved in a shorter time and at lower temperatures (Varma, 2007; Dudley et al, 2015). Other authors also used TBHP (Choudhary and Dumbre, 2009a,b, 2010; Choudhary et al, 2009; Li H. R. et al, 2009; Peneau et al, 2013; Zhang B. et al, 2016; Martins et al, 2017; Ndolomingo and Meijboom, 2017; Gogoi et al, 2018; Kashani et al, 2018) and H 2 O 2 (Zhan et al, 2012, 2013; Hallett-Tapley et al, 2013; Moreno et al, 2013; Santonastaso et al, 2014; Tang et al, 2014; Long and Quan, 2015; Mehri et al, 2015; Restrepo et al, 2015a,b; Emayavaramban et al, 2016a; Zhang B. et al, 2016; Gogoi et al, 2018; Khawaji and Chadwick, 2018; Tareq et al, 2018) as oxidants for alcohol oxidation reactions, although more studies deal with the use of oxygen (Besson and Gallezot, 2000; Prati and Porta, 2005; Bond et al, 2006; Hashmi and Hutchings, 2006; Hutchings et al, 2006; Carabineiro and Thompson, 2007, 2010; Ishida and Haruta, 2007; Fristrup et al, 2008; Della Pina and Falletta, 2011; Della Pina et al, 2012; Dimitratos et al, 2012; Takei et al, 2012; Hutchings, 2014; Freakley et al, 2015; Sharma et al, 2016).…”