Nomura has downgraded its rating for oil major Royal Dutch Shell from 'buy' to 'neutral', saying that there's an absence of clear positive catalysts."In conjunction with our upgrade of Total, we lower our rating for Shell. We do little to our estimates except mark to market for Q2 numbers. We do not think Shell is expensive, but we cannot say it is at a significant discount to the European oil sector either," the broker said in a research report out Wednesday evening.Shell trades at 7.9 times 2014 earnings, slightly below the sector-average multiple of 8.1%, and offers a dividend yield of 5.3% (sector: 5.6%).Nomura said that the firm is in a "period of construction" after a new four-year plan was announced last year, as it looks to deliver multiple projects to meet 2015 cash flow targets. The broker said it was concerned the transition "may be a little more pronounced" while the market waits for messages from incoming Chief Executive Officer Ben van Beurden who is due to replace Peter Voser early next year."The crux of the investment case remains the balance between the level of capital investment and its allocation versus cash return to shareholders," the broker said. "In the context of Big Oil, Shell's business model remains defensive and more adaptable than most to a range of macro scenarios. However, with Shell largely limited to the B line on the buy-back for tax reasons and a framework that sees capex rise in 2014/15, we see it as difficult for the shares to materially outperform during H2 in the absence of a marked fall in oil prices and/or equity markets."With the benefits of earnings integration from Pearl GTL (gas-to-liquids) plant in Qatar earlier this year now priced in, Nomura sees little scope for positive near-term momentum and thinks that the shares will "tread water" until the evidence of project delivery is seen next year.The target price for the stock has been cut from 2,500p to 2,400p.BC