Heterogeneous Bifunctional Metal/Acid Catalysts for Selective Chemical Processes

Abstract

Heterogeneous catalysts enabling multiple reaction sequences in one pot have a great potential for large‐scale production processes in terms of productivity, cost‐effectiveness, and low environmental impact. This paper reviews the most representative examples and the recent achievements in the field of solid bifunctional metal/acid‐site catalysts and their application to the production of fine chemicals through selective, cooperative, or sequential processes in single reactor units. The literature that appeared from January 2009 to January 2012 is covered.

One‐Step Approach to 2,5‐Diformylfuran from Fructose by Using a Bifunctional and Recyclable Acidic Polyoxometalate Catalyst

“…According to reports in the literature, the relative reactivity of the VO x and MoO x cations in the MVP-HPA (H 3+x PMo 12Àx V x O 40 ) Keggin structure is VO x @ MoO x for methanol oxidation to formaldehyde. [42,43] This reactivity trend is related to greater electron delocalization introduced by incorporation of the VO x units into MVP-HPA; moreover, the extent of structural disorder in the MVP-HPA Keggins increases with the number of incorporated VO x units. In principle, our reported results seem to agree with the above conclusion, and indicate that the increase in the vanadium content of CsMVP-HPA catalysts promotes catalytic performance for the aerobic oxidation of HMF to DFF (Table 1) Unfortunately, the increased vanadium content in CsMVP-HPA simultaneously decreases the acid density of the catalyst, which results in a decreased catalytic performance of CsMVP-HPA for the dehydration of fructose to HMF (Table 1).…”

“…[41] Inspired by these studies, we thus thought it would be promising to explore an efficient, recyclable, and bifunctional catalyst for fructose-to-HMF transformation when compared with a combined dual catalytic system. [42,43] Molybdovanadophosphoric heteropolyacid (MVP-HPA) is an ideal candidate catalyst for a one-pot approach to DFF from fructose owing to its unique bifunctional catalytic nature both for acidity and redox properties. [44] However, MVP-HPA functions homogeneously in most liquid phases, and the separation and recovery of MVP-HPA from the reaction medium is problematic.…”

Electrochemically Fabricated Ni−P, Ni−S and Ni−Se Materials for Overall Water Splitting: Investigating the Concept of Bifunctional Electrocatalysis

“…Bifunctional catalysis in the homogeneous catalysis area uses molecules that possess two distinct functional groups to bring about new reactivity and/or selectivity to a reaction of interest . For heterogeneous catalysis the principle is the same and as an example a bifunctional catalyst may combine a supported acid and metal site that can promote reactions typical of organic catalysis such as hydrolysis and condensation with the characteristics of metal‐mediated activators such as hydrogenation or oxidation reactions in cascade or that act in a cooperative way …”

“…[9] For heterogeneous catalysis the principle is the same and as an example a bifunctional catalyst may combine a supported acid and metal site that can promote reactions typical of organic catalysis such as hydrolysis and condensation with the characteristics of metal-mediated activators such as hydrogenation or oxidation reactions in cascade or that act in a cooperative way. [10] In electrocatalysis the term appears to be used rather differently and attributed to materials that may exhibit both HER and OER activity without considering in many cases what compositional and/or structural changes may occur during the catalytic process. Therefore, should a material be classified as bifunctional if it is simply active for HER and OER or should a material maintain its activity for both reactions if switched between the HER and OER without any degradation in performance for both reactions?…”

Confinement Effects in Zeolite‐Confined Noble Metals

“…Zeolites can provide as pecific platform for nanometals, for example,p rotective microenvironments and functional sites for catalytic reactions.F or example,c ombined with noble metal sites,a cidic zeolites enable dual-site catalysts capable of catalyzing different types of reactions on dual active metal and acid sites (Figure 6a,i nset). [114][115][116] Dual-site catalysts usually have unique properties due to the synergy between metals and acidic functions. [117] Generally,inac atalytic reaction, the confined noble metal in the acidic zeolite will strongly influence the state of the acid sites.F or example, Pt and Ir metal nanoparticles became involved in charge transfer with neighboring framework atoms of Beta and Y zeolites and thus affected the mean framework electronegativity of the zeolites as was shown by 1 Hmagic-angle spinning (MAS) NMR and FTIR spectroscopy.…”