The Direct Synthesis of H₂O₂ Using TS‐1 Supported Catalysts

Abstract

In this study we show that using AuPd nanoparticles supported on a commercial titanium silicate (TS-1) prepared using a wet co-impregnation method it is possible to produce hydrogen peroxide from molecular H 2 and O 2 via the direct synthesis reaction. The effect of Au: Pd ratio and calcination temperature is evaluated as well as the role of Pt addition to the AuPd supported catalysts. The effect of Pt addition to AuPt nanoparticles is observed to result in a significant improvement in catalytic activity and selectivity to hydrogen peroxide with detailed characterisation indicating this is a result of selectively tuning the ratio of Pd oxidation states.

The Direct Synthesis of H2O2 and Selective Oxidation of Methane to Methanol Using HZSM-5 Supported AuPd Catalysts

“…Evaluation of catalyst activity upon re-use revealed that when calcined at 400 °C catalytic activity decreased to 35 mol H2O2 kg −1 cat h −1 but remained stable upon second use, which is in keeping with our previous studies into AuPd catalysts supported on TiO 2 [39] and TS-1 [23]. This loss in catalytic activity is attributed to leaching of active metals from the support with significant loss of both Au and Pd observed via MP-AES analysis for catalysts exposed to calcination temperatures below 400 °C.…”

“…However, the activity of the 0.5%Au-0.5%Pd/HZSM-5(30) catalyst does not supersede that of the 1%Pd/HZSM-5(30) catalyst, with the enhanced activity of bi-metallic AuPd nanoparticles previously observed to offer greater activity than the analogous Pd-only catalyst when utilising a range of oxide supports [48][49][50]. We attribute this to a lack of complete alloying and only partial formation of the Au-core PdO-shell typically adopted on oxide supports, indeed this is in keeping with our previous studies investigating the catalytic activity of AuPd catalysts supported on SiO 2 [51] and TS-1 [23]. It should be noted that catalytic activity of AuPd supported nanoparticles on HZSM-5(30) is significantly less active than that observed for the analogous catalyst supported on TiO 2 , with this believed to be related to formation of the Au-core PdO-shell morphology adopted when utilising TiO 2 as a support.…”

“…As with this previous study we report an enhancement in H 2 O 2 utilisation with increasing calcination temperature the extent of H 2 O 2 conversion decreases from 42.6 to 39.5%. We ascribe this to a combination of the improved H 2 O 2 selectivity of larger AuPd nanoparticles [23,60], known to form at higher calcination temperatures, and an increase in Pd: Au ratio, as determined by XPS (Table 6). With the latter indicating the possible enhancement of Au-core PdO-shell morphology known to be key in achieving high rates of H 2 O 2 selectivity.…”

“…As seen in Table 8 catalytic selectivity towards methanol can be related to Al 2 O 3 content, with the 0.5%Au-0.5%Pd/ HZSM-5(23) catalyst observed to offer the highest selectivity towards methanol (51.8%). As Al 2 O 3 content decreases so too does catalytic selectivity towards methanol, with selectivity observed over the 0.5%Au-0.5%Pd/HZSM-5(280) (22.9%) catalyst less than half that of the analogous catalyst supported on HZSM-5 (23), which is in keeping with previous work by Kalamaras et al [64] The means by which a high Al 2 O 3 content can enhance catalytic performance for the selective oxidation of methane is still of some debate. However, it is possible that the enhanced acidity of the support results in improved selectivity towards H 2 O 2 , with the enhanced stability of H 2 O 2 over acidic supports well known [52].…”

“…We [21][22][23] have previously reported the efficacy of AuPd nanoparticles supported on a range of zeolites, for the production of H 2 O 2 as well as their use in the oxidation of cyclohexene and 2-butenol [24]. Further work has demonstrated the feasibility of in situ H 2 O 2 generation in the hydroxylation of benzene [25,26] and cyclohexane [27].…”